Free-cutting copper alloy and method for manufacturing free-cutting copper alloy

ABSTRACT

This free-cutting copper alloy includes Cu: more than 61.0% and less than 65.0%, Si: more than 1.0% and less than 1.5%, Pb: 0.003% to less than 0.20%, and P: more than 0.003% and less than 0.19%, with the remainder being Zn and unavoidable impurities, a total content of Fe, Mn, Co, and Cr is less than 0.40%, a total content of Sn and Al is less than 0.40%, a relationship of 56.5≤f1=[Cu]−4.5×[Si]+0.5×[Pb]−[P]≤59.5 is satisfied, constituent phases of a metallographic structure have relationships of 20≤(α)≤80, 15≤(β)≤80, 0≤(γ)&lt;8, 18×(γ)/(β)&lt;9, 20≤(γ)1/2×3+(β)×([Si])1/2≤88, and 33≤(γ)1/2×3+(β)×([Si])1/2+([Pb])1/2×35+([P])1/2×15, and a compound including P is present in β phase.

TECHNICAL FIELD

The present invention relates to a free-cutting copper alloy having ahigh strength and a significantly reduced Pb content and a method forproducing a free-cutting copper alloy. The present invention relates toa free-cutting copper alloy used for automobile components, electricaland electronic apparatus components, mechanical components,stationaries, toys, sliding components, measuring instrument components,precision mechanical components, medical components, drink-relateddevices and components, devices and components for water drainage,industrial plumbing components, or components relating to liquid or gassuch as drinking water, industrial water, drainage water, or hydrogen,and a method for producing the free-cutting copper alloy. Examples ofspecific component names include valves, joints, cocks, faucets, gears,axles, bearings, shafts, sleeves, spindles, sensors, bolts, nuts, flarenuts, pen points, insert nuts, cap nuts, nipples, spacers, and screws.The present invention relates to a free-cutting copper alloy used forthe components that are made by machining, and a method for producingthe free-cutting copper alloy.

The present application claims priority on Japanese Patent ApplicationNo. 2019-116914 filed on Jun. 25, 2019, Japanese Patent Application No.2019-130143 filed on Jul. 12, 2019, Japanese Patent Application No.2019-141096 filed on Jul. 31, 2019, and Japanese Patent Application No.2019-163773 filed on Sep. 9, 2019, the contents of which areincorporated herein by reference.

BACKGROUND ART

Conventionally, a Cu—Zn—Pb alloy (so-called a free-cutting brass bar,brass for forging, or brass for casting) or a Cu—Sn—Zn—Pb alloy(so-called bronze casting: gunmetal) having excellent machinability hasbeen generally used for components such as valves, joints, gears,sensors, nuts, or screws that are specific component names of automobilecomponents, electrical, home appliance, and electronic apparatuscomponents, mechanical components, stationaries, precision mechanicalcomponents, medical components, or devices and components relating toliquid or gas such as drinking water, industrial water, drainage water,or hydrogen.

A Cu—Zn—Pb alloy includes 56% to 65 mass % Cu, 1% to 4 mass % Pb, andthe balance being Zn. A Cu—Sn—Zn—Pb alloy includes 80% to 88 mass % Cu,2% to 8 mass % Sn, 1% to 8 mass % Pb, and the balance being Zn.

Pb added to copper alloy has a tremendous effect particularly in ahole-making process particularly using a drill. Recently, the dimensionsof various devices and components have decreased, and the necessity ofdrilling tiny holes on such components has increased. It is expectedthat a reduction in the size of various industrial components such ashome information appliances, medical devices, or automobile componentswill be accelerated.

However, recently, Pb's influence on human body and the environment isbecoming a concern, and momentum to regulate Pb is increasing in variouscountries. For example, a regulation for reducing the Pb content indrinking water supply devices to be 0.25 mass % or lower came into forcein January 2010 in California, the United States. In countries otherthan the United States also, such regulation is rapidly beingestablished, and development of a copper alloy material that meets therequirements of the regulation on Pb content is in demand.

In addition, in other industrial fields such as those of automobiles,electrical and electronic apparatuses, and machines, for example, in ELVregulations and RoHS regulations of the Europe, free-cutting copperalloys are exceptionally allowed to include maximum 4 mass % Pb.However, like in the field of drinking water, strengthening ofregulations on Pb content including elimination of exemptions has beenactively discussed.

While there is a trend to strengthen Pb regulations for free-cuttingcopper alloys, alloys like (1) a Cu—Zn—Bi alloy or Cu—Zn—Bi—Se alloyincluding Bi having machinability (machining performance,machinability-improvement function) or, in some cases, including notonly Bi but also Se instead of Pb, (2) a Cu—Zn alloy including a highconcentration of Zn in which the amount of β phase is increased toimprove machinability, (3) a Cu—Zn—Si alloy or Cu—Zn—Sn alloy includinglarge amounts of γ phase and κ phase having machinability instead of Pb,(4) a Cu—Zn—Sn—Bi alloy including a large amount of γ phase and Bi, etc.are proposed.

Patent Document 1 discloses a method of improving machinability andcorrosion resistance by adding 0.7% to 2.5 mass % Sn to a Cu—Zn—Bi alloysuch that γ phase precipitates.

However, alloys including Bi instead of Pb have many problems. Forexample, Bi has lower machinability than Pb. Bi may be harmful to humanbody like Pb. Bi has a resourcing problem because it is a rare metal.And, Bi embrittles a copper alloy material.

In addition, as disclosed in Patent Document 1, even when γ phase of aCu—Zn—Sn alloy is precipitated, γ phase including Sn has poormachinability, thus requiring co-addition of Bi having machinability.

On the one hand, it is absolutely impossible to replace a free-cuttingcopper alloy containing lead with a Cu—Zn binary alloy including a largeamount of β phase since even though β phase contributes to improvementof machinability, it has lower machinability than Pb. On the other hand,Cu—Zn—Si alloys including Si instead of Pb are proposed as free-cuttingcopper alloys in, for example, Patent Documents 2 to 13.

In Patent Documents 2 and 3, excellent machinability is realized withoutincluding Pb or with a small amount of Pb by the excellent machinabilityof γ phase, or, in some cases, κ phase formed in an alloy mainlycomprising a high Cu concentration of 69% to 79 mass % and a high Siconcentration of 2 to 4 mass %. By including greater than or equal to0.3 mass % Sn and greater than or equal to 0.1 mass % Al, formation of γphase having machinability is further increased and accelerated suchthat machinability can be improved. Corrosion resistance is improved byforming a large amount of γ phase.

In Patent Document 4, excellent machinability is obtained by adding anextremely small amount (0.02 mass % or lower) of Pb and simply definingthe total area of γ phase and κ phase mainly in consideration of the Pbcontent.

Patent Documents 5 and 6 propose casting products of Cu—Zn—Si alloys inwhich, in order to reduce the size of crystal grains of the casting,extremely small amounts of P and Zr are included, and recite that theP/Zr ratio and the like are important.

Patent Document 7 proposes a copper alloy in which Fe is included in aCu—Zn—Si alloy.

Patent Document 8 proposes a copper alloy in which Sn, Fe, Co, Ni, andMn are included in a Cu—Zn—Si alloy.

Patent Document 9 proposes a Cu—Zn—Si alloy having an a phase matrixincluding κ phase in which area ratios of β phase, γ phase, and μ phaseare limited.

Patent Document 10 proposes a Cu—Zn—Si alloy having an a phase matrixincluding κ phase in which area ratios of β phase and γ phase arelimited.

Patent Document 11 proposes a Cu—Zn—Si alloy in which the length of thelonger sides of γ phase and the length of the longer sides of μ phaseare defined.

Patent Document 12 proposes a Cu—Zn—Si alloy to which Sn and Al areadded.

Patent Document 13 proposes a Cu—Zn—Si alloy in which γ phase isdistributed in the form of particles at a phase boundary between a phaseand β phase to improve machinability.

Patent Document 15 proposes a Cu—Zn alloy to which Sn, Pb, and Si areadded.

Now, as described in Patent Document 14 and Non-Patent Document 1, inCu—Zn—Si alloys, it is known that, even when looking at only thosehaving Cu concentration of 60 mass % or higher, a Zn concentration of 40mass % or lower, and Si concentration of 10 mass % or lower, 10 kinds ofmetallic phases including α phase matrix, β phase, γ phase, δ phase, εphase, ζ phase, η phase, κ phase, μ phase, and χ phase, in some cases,13 kinds of metallic phases including additional phases of α′, β′, andγ′ are present. Further, it is empirically known that, as the number ofadditive elements increases, the metallographic structure becomescomplicated, and a new phase or an intermetallic compound may appear. Inaddition, it is also empirically well known that there is a largedifference in the constitution of metallic phases between what anequilibrium phase diagram shows and that of an actually produced alloy.Further, it is well known that the composition of these phases changesdepending on the concentrations of Cu, Zn, Si, and the like in a copperalloy and processing heat history.

Incidentally, in Cu—Zn—Pb alloys including Pb, the Cu concentration isabout 60 mass % whereas in all the Cu—Zn—Si alloys described in PatentDocuments 2 to 13, the Cu concentrations are 65 mass % or higher, and areduction in the concentration of expensive Cu is desired from aviewpoint of economic efficiency.

In addition, for conventional leaded free-cutting copper alloys, it isexpected that machining such as turning or drilling can be performedwithout troubles for at least 24 hours and without replacement ofcutting tool or adjustment such as polishing of cutting edge for 24hours. Although depending on the degree of difficulty of machining, thesame level of machinability is expected for alloys containing asignificantly reduced amount of Pb.

Further, in Patent Document 7, the Cu—Zn—Si alloy includes Fe, and Feand Si form an intermetallic compound of Fe—Si which is harder and morebrittle than γ phase. This intermetallic compound has problems likereducing tool life of a cutting tool during machining and generation ofhard spots during polishing impairing the external appearance. Inaddition, since Fe combines with Si which is an additive element and Siis thus consumed as an intermetallic compound, the performance of thealloy deteriorates.

In addition, in Patent Document 8, Sn, Fe, Co, and Mn are added to aCu—Zn—Si alloy. However, Fe, Co, and Mn all combine with Si to form ahard and brittle intermetallic compound. Therefore, such addition causesproblems during machining or polishing as disclosed by Patent Document7.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: PCT International Publication No. WO2008/081947-   Patent Document 2: Japanese Unexamined Patent Application, First    Publication No. 2000-119775-   Patent Document 3: Japanese Unexamined Patent Application, First    Publication No. 2000-119774-   Patent Document 4: PCT International Publication No. WO2007/034571-   Patent Document 5: PCT International Publication No. WO2006/016442-   Patent Document 6: PCT International Publication No. WO2006/016624-   Patent Document 7: Published Japanese Translation No. 2016-511792 of    the PCT International Publication-   Patent Document 8: Japanese Unexamined Patent Application, First    Publication No. 2004-263301-   Patent Document 9: PCT International Publication No. WO2012/057055-   Patent Document 10: Japanese Unexamined Patent Application, First    Publication No. 2013-104071-   Patent Document 11: PCT International Publication No. WO2019/035225-   Patent Document 12: Japanese Unexamined Patent Application, First    Publication No. 2018-048397-   Patent Document 13: Published Japanese Translation No. 2019-508584    of the PCT International Publication-   Patent Document 14: U.S. Pat. No. 4,055,445-   Patent Document 15: Japanese Unexamined Patent Application, First    Publication No. 2016-194123

Non-Patent Document

-   Non-Patent Document 1: Genjiro MIMA, Masaharu HASEGAWA, Journal of    the Japan Copper and Brass Research Association, 2 (1963), p. 62 to    77

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

The present invention has been made in order to solve theabove-described problems in the conventional art, and an object thereofis to provide a free-cutting copper alloy having excellent hotworkability, a high strength, a good balance between strength andductility, and excellent toughness whose Pb content has beensignificantly reduced, and a method for producing the free-cuttingcopper alloy.

In this specification, unless specified otherwise, a hot worked materialincludes a hot extruded material, a hot forged material, and a hotrolled material. Cold workability refers to performance of cold workingsuch as drawing, wire drawing, rolling, crimping, or bending. Drillingrefers to making holes with a drill. Unless specified otherwise,excellent machinability refers to low cutting resistance and good orexcellent chip breakability during turning with a lathe or drilling.Conductivity refers to electric conductivity and thermal conductivity.In addition, β phase includes β′ phase, γ phase includes γ′ phase, and aphase includes α′ phase. Cooling rate refers to the average cooling ratein a given temperature range. 24 hours refer to one day. “Manufacturingon the actual production line” refers to production with a massproduction facility used for manufacturing products for sale.P-containing compound is a compound including P and at least either Sior Zn or both Si and Zn, in some cases, further including Cu and/orinevitable impurities such as Fe, Mn, Cr, or Co. P-containing compoundcan be a compound such as P—Si, P—Si—Zn, P—Zn, or P—Zn—Cu. P-containingcompound also refers to a compound including P, Si, and Zn.

Solutions for Solving the Problems

In order to solve the above-described problems and to achieve theabove-described object, the present inventors conducted a thoroughinvestigation and obtained the following findings.

Patent Documents 4 and 6 disclose that in Cu—Zn—Si alloys, β phase doesnot substantially contribute to machinability of the alloy, but ratherinhibits it. Patent Documents 2 and 3 recite that when β phase ispresent, β phase is changed into γ phase by heat treatment. In PatentDocuments 9, 10, and 11, also, the amount of β phase is significantlylimited. Patent Document 15 discloses that, in order to improvedezincification corrosion resistance of β phase, it is necessary that Snand Si are included, that hot extrusion is performed at a temperature of700° C. or higher, and that a heat treatment in which holdingtemperature is 400° C. to 600° C. and the average cooling rate from 400°C. to 200° C. is 0.2° C./sec to 10° C./sec is performed.

First, the present inventors diligently studied β phase that had beenknown to have no effect on machinability of a Cu—Zn—Si alloy in theconventional art, and found out the composition of β phase that has alarge effect on machinability.

However, there still was a significant difference in machinability interms of chip breakability and cutting resistance if compared with afree-cutting brass including 3 mass % Pb even if β phase contains Si, anelement that has a large effect on machinability.

Therefore, in order to improve the machinability (machining performance,machinability-improvement function) of β phase itself, a compoundincluding P and Si and/or Zn having a size of about 0.5 to 3 μm (forexample, P—Si, P—Si—Zn, P—Zn, or P—Zn—Cu) was made to precipitate in βphase of a Cu—Zn—Si alloy including an appropriate amount of Si. As aresult, the machinability of β phase dramatically improved.

However, β phase with improved machinability has poor ductility andtoughness. In order to improve ductility without deterioration of themachinability of β phase, the amounts of β phase and α phase werecontrolled to appropriate levels, and distributions of α phase and βphase, and shapes of crystal grains of a phase were controlled.

A copper alloy having machinability comparable to that of a conventionalcopper alloy including a large amount of Pb was thus invented by makingthe copper alloy include β phase having further improved machinability,a phase having excellent ductility, a small amount of Pb, andoptionally, a small amount of γ phase.

A free-cutting copper alloy according to a first aspect of the presentinvention includes: higher than 61.0 mass % and lower than 65.0 mass %of Cu; higher than 1.0 mass % and lower than 1.5 mass % of Si; higherthan or equal to 0.003 mass % and lower than 0.20 mass % of Pb; andhigher than 0.003 mass % and lower than 0.19 mass % of P, with thebalance being Zn and inevitable impurities,

in which, among the inevitable impurities, a total content of Fe, Mn,Co, and Cr is lower than 0.40 mass % and a total content of Sn and Al islower than 0.40 mass %, when a Cu content is represented by [Cu] mass %,a Si content is represented by [Si] mass %, and a Pb content isrepresented by [Pb] mass %, the following relationship of

56.5 ≤ f 1 = [Cu] − 4.5 × [Si] + 0.5 × [Pb] − [P] ≤ 59.5

is satisfied,

in constituent phases of a metallographic structure excludingnon-metallic inclusions, when an area ratio of α phase is represented by(α)%, an area ratio of γ phase is represented by (γ)%, and an area ratioof β phase is represented by (β)%, the following relationships of

20 ≤ (α) ≤ 80, 15 ≤ (β) ≤ 80, 0 ≤ (γ) < 8, 18 × (γ)/(β) < 9, 20 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) ≤ 88, and  33 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) + ([Pb])^(1/2) × 35 + ([P])^(1/2) × 15

are satisfied, and

a P-containing compound is present in the β phase.

A free-cutting copper alloy according to a second aspect of the presentinvention includes: higher than or equal to 61.7 mass % and lower thanor equal to 64.3 mass % of Cu; higher than or equal to 1.02 mass % andlower than or equal to 1.35 mass % of Si; higher than or equal to 0.005mass % and lower than or equal to 0.10 mass % of Pb; and higher than orequal to 0.02 mass % and lower than or equal to 0.14 mass % of P, withthe balance being Zn and inevitable impurities,

in which among the inevitable impurities, a total content of Fe, Mn, Co,and Cr is lower than or equal to 0.30 mass % and a total content of Snand Al is lower than or equal to 0.30 mass %,

when a Cu content is represented by [Cu] mass %, a Si content isrepresented by [Si] mass %, and a Pb content is represented by [Pb] mass%, the following relationship of

57.0 ≤ f 1 = [Cu] − 4.5 × [Si] + 0.5 × [Pb] − [P] ≤ 59.0

is satisfied,

in constituent phases of a metallographic structure excludingnon-metallic inclusions, when an area ratio of α phase is represented by(α)%, an area ratio of γ phase is represented by (γ)%, and an area ratioof β phase is represented by (β)%, the following relationships of

30 ≤ (α) ≤ 75, 25 ≤ (β) ≤ 70, 0 ≤ (γ) < 4, 18 × (γ)/(β) < 2, 30 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) ≤ 77, and44 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) + ([Pb])^(1/2) × 35 + ([P])^(1/2) × 15

are satisfied, and

a P-containing compound is present in the β phase.

A free-cutting copper alloy according to a third aspect of the presentinvention is the free-cutting copper alloy according to the first orsecond aspect of the present invention, in which a proportion ofgranular α phase crystal grains having an aspect ratio (longerside/shorter side) of lower than or equal to 4 is higher than or equalto 50%.

A free-cutting copper alloy according to a fourth aspect of the presentinvention is the free-cutting copper alloy according to any one of thefirst to third aspects of the present invention, in which a Si contentin β phase is higher than or equal to 1.2 mass % and lower than or equalto 1.9 mass %.

A free-cutting copper alloy according to a fifth aspect of the presentinvention is the free-cutting copper alloy according to any one of thefirst to fourth aspects of the present invention, in which an electricalconductivity is higher than or equal to 13% IACS, and when a tensilestrength is represented by S (N/mm²) and an elongation is represented byE (%), a relational expression S×(100+E)/100 indicating a balancebetween the strength and the elongation is higher than or equal to 600.

A free-cutting copper alloy according to a sixth aspect of the presentinvention is the free-cutting copper alloy according to any one of thefirst to fifth aspects of the present invention, which is used for anautomobile component, an electrical or electronic apparatus component, amechanical component, a stationery, a toy, a sliding component, ameasuring instrument component, a precision mechanical component, amedical component, a drink-related device or component, a device orcomponent for water drainage, or an industrial plumbing component.

A method for producing a free-cutting copper alloy according to aseventh aspect of the present invention is a method for producing thefree-cutting copper alloy according to any one of the first to sixthaspects of the present invention, including one or more hot workingsteps, in which in the final hot working step among the hot workingsteps, hot working temperature is higher than 540° C. and lower than675° C., and an average cooling rate in a temperature range from 530° C.to 450° C. after hot working is higher than or equal to 0.1° C./min andlower than or equal to 50° C./min.

A method for producing a free-cutting copper alloy according to aneighth aspect of the present invention is the method for producing afree-cutting copper alloy according to the seventh aspect of the presentinvention, further including one or more steps selected from a coldworking step, a straightness correction step, and an annealing step.

A method for producing a free-cutting copper alloy according to a ninthaspect of the present invention is the method for producing afree-cutting copper alloy according to the seventh or eighth aspect ofthe present invention, further including a low-temperature annealingstep that is performed after the final step among the hot working step,the cold working step, the straightness correction step, and theannealing step, in which in the low-temperature annealing step, holdingtemperature is higher than or equal to 250° C. and lower than or equalto 430° C., and holding time is longer than or equal to 10 minutes andshorter than or equal to 200 minutes.

Effects of Invention

According to one aspect of the present invention, a free-cutting copperalloy having excellent hot workability, a high strength, a good balancebetween strength and ductility, and excellent toughness and containing asignificantly reduced amount of Pb, and a method for producing thefree-cutting copper alloy can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a picture showing the structure of a free-cutting copperalloy according to an embodiment, which includes 62.9 mass % Cu, 1.14mass % Si, 0.072 mass % P, 0.009 mass % Pb, and Zn as the balance and isobtained by hot extrusion at 590° C. and cooling at an average coolingrate of 25° C./min in a temperature range from 530° C. to 450° C.

FIG. 1B is a picture showing the structure of a free-cutting copperalloy according to an embodiment, which includes 62.9 mass % Cu, 1.14mass % Si, 0.072 mass % P, 0.009 mass % Pb, and Zn as the balance and isobtained by hot forging at 615° C. and cooling at an average coolingrate of 28° C./min in a temperature range from 530° C. to 450° C.

FIG. 1C is a picture showing the structure of a free-cutting copperalloy according to an embodiment, which includes 62.5 mass % Cu, 1.05mass % Si, 0.001 mass % P, 0.016 mass % Pb, and Zn as the balance and isobtained by hot extrusion at 595° C. and cooling at an average coolingrate of 25° C./min in a temperature range from 530° C. to 450° C.

FIG. 2A is a picture of chips after performing a machining test of TestNo. T01 among the Examples.

FIG. 2B is a picture of chips after performing a machining test of TestNo. T303 among the Examples.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Below is a description of free-cutting copper alloys according to theembodiments of the present invention and methods for producing thefree-cutting copper alloys.

The free-cutting copper alloys according to the embodiments are used forautomobile components, electrical components, home appliance components,and electronic components, mechanical components, and devices andcomponents that come in contact with liquid or gas such as drinkingwater, industrial water, or hydrogen. Examples of specific componentnames include valve, joint, gear, screws nut, sensor, and pressurevessel.

Here, in this specification, an element symbol in parentheses such as[Zn] represents the content (mass %) of the element.

In the embodiment, using this content expressing method, a compositionrelational expression f1 is defined as follows.

Composition relational expression f1=[Cu]−4.5×[Si]+0.5×[Pb]−[P]

Further, in the embodiment, in constituent phases of the metallographicstructure excluding non-metallic inclusions, the area ratio of a phaseis represented by (α)%, the area ratio of γ phase is represented by(γ)%, and the area ratio of β phase is represented by (β)%. The arearatio of each of the phases will also be referred to as “the amount ofeach of the phases”, “the proportion of each of the phases”, or “theproportion that each of the phases occupies”.

In the embodiments, a plurality of metallographic structure relationalexpressions are defined as follows.

Metallographic Structure Relational Expression f2=(α)

Metallographic Structure Relational Expression f3=(β)

Metallographic Structure Relational Expression f4=(γ)

Metallographic Structure Relational Expression f5=18×(γ)/(β)

Metallographic Structure Relational Expressionf6=(γ)^(1/2)×3+(β)×([Si])^(1/2)

Metallographic Structure and Composition Relational Expressionf6A=(γ)^(1/2)×3+(β)×([Si])^(1/2)+([Pb])^(1/2)×35+([P])^(1/2)×15

A free-cutting copper alloy according to the first embodiment of thepresent invention includes: higher than 61.0 mass % and lower than 65.0mass % Cu; higher than 1.0 mass % and lower than 1.5 mass % Si; higherthan or equal to 0.003 mass % and lower than 0.20 mass % Pb; higher than0.003 mass % and lower than 0.19 mass % P; and the balance comprising Znand inevitable impurities, in which the total content of Fe, Mn, Co, andCr is lower than 0.40 mass %, the total content of Sn and Al is lowerthan 0.40 mass %, the composition relational expression f1 is in a rangeof 56.5 f1≤59.5, the metallographic structure relational expression f2is in a range of 20≤f2≤80, the metallographic structure relationalexpression f3 is in a range of 15≤f3≤80, the metallographic structurerelational expression f4 is in a range of 0≤f4<8, the metallographicstructure relational expression f5 is in a range of f5<9, themetallographic structure relational expression f6 is in a range of20≤f6≤88, the metallographic structure and composition relationalexpression f6A is in a range of f6A≥33, and a P-containing compound ispresent in β phase.

A free-cutting copper alloy according to the second embodiment of thepresent invention includes: greater than or equal to 61.7 mass % andlower than or equal to 64.3 mass % Cu; greater than or equal to 1.02mass % and lower than or equal to 1.35 mass % Si; greater than or equalto 0.005 mass % and lower than or equal to 0.10 mass % Pb; greater thanor equal to 0.02 mass % and lower than or equal to 0.14 mass % P; andthe balance comprising Zn and inevitable impurities, in which the totalcontent of Fe, Mn, Co, and Cr is 0.30 mass % or lower and the totalcontent of Sn and Al is 0.30 mass % or lower, the composition relationalexpression f1 is in a range of 57.0≤f1≤59.0, the metallographicstructure relational expression f2 is in a range of 30≤f2≤75, themetallographic structure relational expression f3 is in a range of25≤f3≤70, the metallographic structure relational expression f4 is in arange of 0≤f4<4, the metallographic structure relational expression f5is in a range of f5<2, the metallographic structure relationalexpression f6 is in a range of 30≤f6≤77, the metallographic structureand composition relational expression f6A is in a range of f6A≥44, and aP-containing compound is present in the β phase.

Here, in the free-cutting copper alloy according to the first or secondembodiment of the present invention, it is preferable that theproportion (proportion to the entirety of α phase) of granular α phasecrystal grains having an aspect ratio (longer side/shorter side) of 4 orlower is 50% or higher. To be exact, the proportion of the granular αphase crystal grains refers to the proportion of the number of granularα phase crystal grains having an aspect ratio of 4 or lower as anumerator to the total number of α phase crystal grains as a denominatorin one visual field, and can be expressed with: (the number of granularα phase crystal grains having an aspect ratio of 4 or lower/the totalnumber of a phase crystal grains)×100.

In addition, in the free-cutting copper alloy according to the first orsecond embodiment of the present invention, it is preferable that the Sicontent in β phase is 1.2 mass % or higher and 1.9 mass % or lower.

Further, in the free-cutting copper alloy according to the first orsecond embodiment of the present invention, it is preferable that theelectric conductivity is 13% IACS or higher and 18% IACS or lower, andwhen tensile strength is represented by S (N/mm²) and elongation isrepresented by E (%), characteristic relational expressionf7=S×(100+E)/100 indicating the balance between strength and elongationis 600 or higher.

The reasons why the component composition, the composition relationalexpression f1, the metallographic structure relational expressions f2,f3, f4, f5, and f6, the metallographic structure and compositionrelational expression f6A, the metallographic structure, thecharacteristic relational expression f7, and the like are defined asdescribed above are explained below.

<Component Composition>

(Cu)

Cu is a main element of the free-cutting copper alloy according to theembodiment. In order to achieve the object of the present invention, thefree-cutting copper alloy needs to contain Cu in an amount exceeding61.0 mass % at least. When the Cu content is 61.0 mass % or lower, theproportion of β phase exceeds 80% although depending on the contents ofSi, Zn, P, and Pb and the production process, and as a result, ductilityof the material is poor. Accordingly, the lower limit of the Cu contentis higher than 61.0 mass %, preferably 61.5 mass % or higher, morepreferably 61.7 mass % or higher, and still more preferably 62.0 mass %or higher.

On the other hand, when the Cu content is 65.0 mass % or higher, theproportion of β phase decreases and the proportion of γ phase increasesalthough depending on the contents of Si, Zn, P, and Pb and theproduction process. In some cases, p phase or other phases may alsoappear. As a result, excellent machinability cannot be obtained, andductility and toughness are poor. Accordingly, the Cu content is lowerthan 65.0 mass %, preferably 64.5 mass % or lower, more preferably 64.3mass % or lower, and still more preferably 63.8 mass % or lower.

An object of the embodiment is to provide an alloy having not onlyexcellent machinability but also excellent mechanical characteristicssuch as strength and ductility. When ductility and the balance betweenductility and strength are important, the lower limit of Cu ispreferably 62.3 mass % or higher.

(Si)

Si is a main element of the free-cutting copper alloy according to theembodiment. Si contributes to the formation of metallic phases such as κphase, γ phase, μ phase, β phase, and ζ phase. Si improvesmachinability, strength, high-temperature deformability, wearresistance, and corrosion resistance, in particular, stress corrosioncracking resistance, of the alloy according to the embodiment. Regardingmachinability, the present inventors found out that β phase formed byCu, Zn, and Si contained in the above-described ranges of amounts hasexcellent machinability. Examples of β phase having excellentmachinability include β phase composed of about 61 mass % Cu, about 1.5mass % Si, and about 37.5 mass % Zn. In addition, the present inventorsalso found out that γ phase formed by Cu, Zn, and Si contained in theabove-described ranges of amounts has excellent machinability if β phaseis present. However, as γ phase has a problem in ductility, its contentis limited.

Examples of representative composition of α phase include about 68 mass% Cu, about 1 mass % Si, and about 31 mass % Zn. Although machinabilityof a phase contained in an alloy having a composition within the rangeof the embodiment is also improved by including Si, the degree of theimprovement is far less than that of β phase.

In addition, due to inclusion of Si, α phase and β phase arestrengthened by solid-solubilization. As a result, the alloy isstrengthened, affecting its ductility and toughness. Even thoughinclusion of Si lowers the electrical conductivity of α phase, theelectrical conductivity of the alloy is improved by the formation of βphase.

In order for an alloy to obtain excellent machinability and highstrength, it is necessary to include Si in an amount exceeding 1.0 mass%. The Si content is preferably 1.02 mass % or higher, more preferably1.05 mass % or higher, and still more preferably 1.07 mass % or higher.

On the other hand, when the Si content is excessively high, the amountof γ phase excessively increases. In some cases, μ phase precipitates. γphase has lower ductility and toughness than β phase, deteriorates theductility of the alloy, and causes cutting resistance to increase insome cases. When the amount of γ phase is excessively large, the thrustvalue of drilling increases. An increase in Si content (increasing ofthe Si content) deteriorates the electrical conductivity of the alloy.In the embodiment, in addition to high strength, obtaining excellentductility and toughness as well as good conductivity (since electricalcomponents and the like are included in the intended applications) istargeted. Therefore, the upper limit of the Si content is lower than 1.5mass % and preferably 1.35 mass % or lower. When ductility andconductivity are important, the upper limit of the Si content is morepreferably 1.3 mass % or lower, and still more preferably 1.25 mass % orlower. Although depending on the production process and the Cuconcentration, when the Si content is lower than about 1.3 mass %, theamount of γ phase is less than about 4%. By increasing the proportion ofβ phase, however, excellent machinability can be maintained, and thebalance between strength and ductility becomes excellent.

Regarding hot workability, by containing Si, the hot deformability of αphase and β phase improve and their hot deformation resistancedeteriorates in a temperature range exceeding 500° C. As a result, thehot deformability of the alloy improves, and its deformation resistancedeteriorates. In particular, when Si is contained in excess of 1.0 mass%, the effect is remarkable. The effect is saturated when the Si contentis about 1.4 mass %.

In the case of a slender bar having a diameter of 5 mm or less or aplate having a thickness of 5 mm or less, whether the alloy hasexcellent cold wire drawability and cold rollability is important. Inaddition, after machining, plastic working such as crimping may beperformed. Basically, the better the cold workability, the worse themachinability, and vice versa. It is preferable to further limit the Sicontent or the amount of γ phase, and it is preferable that the Sicontent is about 1.25 mass % or lower or the area ratio of γ phase isabout 1% or lower.

When a base alloy of Cu—Zn binary alloy includes third and fourthelements and the contents of the third and fourth elements increase ordecrease, the properties and characteristics of β phase change. Asdescribed in Patent Documents 2 to 5, β phase present in an alloyincluding greater than or equal to about 69 mass % Cu, greater than orequal to about 2 mass % Si, and the balance being Zn does not have thesame properties or characteristics as β phase present in an alloyaccording to the embodiment, for example, an alloy including about 63mass % Cu, about 1.2 mass % Si, and the balance being Zn. Further, whena large amount of inevitable impurities are included, thecharacteristics of β phase also change. In some cases, propertiesincluding machinability change. Likewise, the characteristics of γ phaseto be present change when the amounts of main elements or the blendingratio between them are changed. Also, when a large amount of inevitableimpurities are included, the characteristics of γ phase change. Further,even when the composition is the same, the kinds of phases to bepresent, their amounts, the distribution of each element in each phasechange depending on the production conditions such as temperature.

(Zn)

Zn is a main element of the free-cutting copper alloy according to theembodiment together with Cu and Si and is an element necessary toenhance machinability, strength, high temperature properties, andcastability. Zn is described as the balance in the composition, but tobe specific, its content is lower than about 37.8 mass % and preferablylower than about 37.5 mass %, and is higher than about 33 mass % andpreferably higher than 33.5 mass %.

(Pb)

In the embodiment, the alloy can obtain good machinability due to βphase including Si. By further including a small amount of Pb, excellentmachinability can be obtained. In the composition according to theembodiment, about 0.001 mass % Pb is solid-solubilized in the matrix,and the rest of the Pb contained in the alloy is present in the form ofPb particles having a diameter of about 0.1 to 3 μm. Pb has a largeeffect on machinability even when its content is small. The effect isexhibited when the Pb content is 0.003 mass % or higher. The Pb contentis preferably 0.005 mass % or higher, more preferably 0.01 mass % orhigher, and still more preferably 0.02 mass % or higher. When machiningconditions are severe, for example, when the cutting speed is high, whenthe feed rate is high, when the cutting depth in turning is deep, orwhen the diameter of a drillhole is large, the Pb content is preferably0.04 mass % or higher and more preferably higher than 0.05 mass %. Byincluding 3 phase having significantly improved machinability and asmall amount of Pb, the machinability of the alloy significantlyimproves.

It is well known that Pb improves machinability of copper alloys. Tothat end, a Cu—Zn binary alloy, a representative one of which is afree-cutting brass bar C3604, needs to include about 3 mass % Pb. In theembodiment, due to β phase including Si, solid solubilization of Pdescribed below, and the presence of P-containing compounds in β phase,β phase, which is a main constituent phase of the alloy according to theembodiment, has machinability substantially comparable to that of C3604.By including a small amount of Pb and causing a small amount of Pbparticles to be present in the metallographic structure, an alloy havingexcellent machinability is accomplished. In consideration of the factthat Pb is harmful to human body and the alloy requires highmachinability, the upper limit of Pb is lower than 0.20 mass %. The Pbcontent is preferably 0.10 mass % or lower and, from a viewpoint ofinfluence on human body and the environment, most preferably 0.08 mass %or lower.

(P)

Regarding P, by solid-solubilization of P in β phase, the machinabilityof 3 phase, that is, the chip breakability of β phase, can be improved,and cutting resistance can be reduced. As a result, the alloy can obtainexcellent machinability. Further, by containing P and adjusting theproduction process, P-containing compounds having an average diameter ofabout 0.5 to 3 μm are formed in β phase. Due to the compounds, in thecase of turning, the three force components—principal cutting force,feed force, and thrust force—decrease. In the case of drilling, thecompounds significantly reduce the torque among others. The three forcecomponents during turning, the torque during drilling, and the chipshape correlate to each other. The smaller the three force componentsand the torque, the more breakable chips get.

P-containing compounds are not formed during hot working. P is mainlysolid-solubilized in β phase during hot working. In the process ofcooling after hot working, P-containing compounds precipitate in β phaseor at a phase boundary between β phase and α phase at a certain criticalcooling rate or lower. The amount of P-containing compounds in a phaseis small. When observed with a metallographic microscope, precipitatesincluding P appear to be granular and have an average particle size ofabout 0.5 to 3 μm. β phase including such precipitate can obtain moreexcellent machinability. Compound including P and also at least eitherone of or both of Si and Zn such as P—Si, P—Si—Zn, P—Zn, or P—Zn—Cuhardly affects the life of a cutting tool and does not substantiallyimpair the ductility or toughness of the alloy. Compound including Fe,Mn, Cr or Co and Si or P contributes to improvement of the strength andwear resistance of the alloy, but consumes Si and P in the alloy, causesthe cutting resistance of the alloy to increase, deteriorates chipbreakability, shortens the tool life, and impairs the ductility.

In order to exhibit the above-described effects, the lower limit of theP content is higher than 0.003 mass %, preferably 0.01 mass % or higher,more preferably 0.02 mass % or higher, and still more preferably 0.03mass % or higher.

When the P content is about 0.015 mass % or higher, P-containingcompounds can be observed with a metallographic microscope. In addition,as the P content increases, the critical cooling rate up to whichP-containing compounds can be formed increases, and the formation ofP-containing compounds is facilitated.

Incidentally, regarding compound including P or Si, for instance, whenthe content of an element that easily combines with Si or P such as Mn,Fe, Cr, or Co increases, the component ratio in the composition of thecompound gradually changes. That is, P-containing compound having asignificant effect of improving the machinability of β phase graduallychanges into a compound having a small effect on machinability.Accordingly, at least the total content of Fe, Mn, Co, and Cr needs tobe limited to less than 0.40 mass % and preferably 0.30 mass % or less.

On the other hand, when the P content is 0.19 mass % or higher,precipitates enlarge, the effect on machinability is saturated,machinability deteriorates instead of improves, and ductility andtoughness also deteriorate. In addition, the Si concentration in β phasemay decrease. Therefore, the P content is lower than 0.19 mass %,preferably 0.14 mass % or lower, and more preferably 0.10 mass % orlower. Even when the P content is about 0.05% or lower than 0.05 mass %,a sufficient amount of the compounds are formed.

(Inevitable Impurities, in Particular, Fe, Mn, Co, and Cr; Sn and Al)

Examples of the inevitable impurities in the embodiment include Mn, Fe,Al, Ni, Mg, Se, Te, Sn, Bi, Co, Ca, Zr, Cr, Ti, In, W, Mo, B, Ag, andrare earth elements.

Conventionally, a free-cutting copper alloy, in particular, free-cuttingbrass including about greater or equal to 30 mass % Zn is not mainlyformed of quality raw material such as electrolytic copper orelectrolytic zinc but is mainly formed of recycled copper alloy. Inpreliminary steps (downstream step, working step) in this field of art,machining is performed on almost all the parts and components, duringwhich a large amount of copper alloy accounting for 40 to 80% of thematerial is disposed of. Examples of such disposed copper alloy includechips, mill ends, burrs, runners, and products having productiondefects. These disposed copper alloys are the main raw material. Ifcutting chips, mill ends, and the like are not properly separated, Pb,Fe, Mn, Si, Se, Te, Sn, P, Sb, As, Bi, Ca, Al, Zr, Ni, and/or rare earthelements mix in raw materials from a leaded free-cutting brass, afree-cutting copper alloy not containing Pb but containing Bi or thelike, a special brass alloy including Si, Mn, Fe, and Al, or othercopper alloys. In addition, cutting chips include Fe, W, Co, Mo, and thelike which originate from tools. Wasted materials include platedproducts, and thus Ni, Cr, and Sn mix in. In addition, Mg, Sn, Fe, Cr,Ti, Co, In, Ni, Se, and Te are mixed into pure copper-based scrap thatis used instead of electrolytic copper. Brass-based scraps that are usedinstead of electrolytic copper or electrolytic zinc are often platedwith Sn, resulting in contamination by a high concentration of Sn.

From a viewpoint of reuse of resources and costs, scraps including theseelements are used as a raw material to the extent that there is no badinfluence on the properties at least. In a leaded JIS free-cutting brassbar, C3604 (JIS H 3250), including about 3 mass % Pb as an essentialelement, Fe may be contained up to 0.5 mass % and Fe+Sn (the totalcontent of Fe and Sn) may be contained up to 1.0 mass % as impurities.Actually, a high concentration of Fe or Sn can be included in afree-cutting brass bar.

Fe, Mn, Co, and Cr are solid-solubilized in a phase, β phase, and γphase of a Cu—Zn alloy to a certain concentration. However, if Si ispresent then, Fe, Mn, Co, and Cr are likely to compound with Si. In somecases, Fe, Mn, Co, and Cr may combine with Si potentially resulting inconsumption of Si that is effective for machinability. Fe, Mn, Co, or Crthat is compounded with Si forms a Fe—Si compound, an Mn—Si compound, aCo—Si compound, or a Cr—Si compound in the metallographic structure.Since these intermetallic compounds are extremely hard, cuttingresistance increases, and the tool life decreases. Therefore, thecontent of each of Fe, Mn, Co, and Cr is required to be limited and ispreferably lower than 0.30 mass %, more preferably lower than 0.20 mass%, and still more preferably 0.15 mass % or lower. In particular, thetotal content of Fe, Mn, Co, and Cr is required to be limited to lowerthan 0.40 mass % and is preferably 0.30 mass % or lower, more preferably0.25 mass % or lower, and still more preferably 0.20 mass % or lower.

On the other hand, Sn and Al mixed in from free-cutting brass, platedwaste products, or the like promote formation of γ phase in the alloyaccording to the embodiment, which is seemingly effective formachinability. However, Sn and Al change the inherent characteristics ofγ phase comprising Cu, Zn, and Si. In addition, larger amounts of Sn andAl are distributed in β phase than in a phase and change characteristicsof β phase. As a result, the alloy's ductility, toughness, ormachinability may deteriorate. Therefore, it is necessary to limit thecontents of Sn and Al. The Sn content is preferably lower than 0.30 mass%, more preferably lower than 0.20 mass %, and still more preferably0.15 mass % or lower. The Al content is preferably lower than 0.20 mass%, more preferably lower than 0.15 mass %, and still more preferably0.10 mass % or lower.

In particular, from a viewpoint of influence on machinability andductility, the total content of Sn and Al is required to be limited tolower than 0.40 mass %, preferably to 0.30 mass % or lower, morepreferably to 0.25 mass % or lower, and still more preferably to 0.20mass % or lower.

As other main inevitable impurity elements, empirically, in many cases,Ni often mixes in from scraps and the like, but the influence onproperties is less than that of Fe, Mn, Sn and the like. Accordingly,the Ni content is preferably lower than 0.3 mass % and more preferablylower than 0.2 mass %. It is not necessary to particularly limit thecontent of Ag because Ag is commonly considered as Cu and does notsubstantially affect various properties. However, the Ag content ispreferably lower than 0.1 mass %. Te and Se themselves have free-cuttingability, and contamination by a large amount of Te and Se may occuralthough it is rare. In consideration of influence on ductility orimpact resistance, the content of each of Te and Se is preferably lowerthan 0.2 mass %, more preferably 0.05 mass % or lower, and still morepreferably 0.02 mass % or lower. In addition, corrosion-resistant brassincludes As and/or Sb in order to improve its corrosion resistance. Inconsideration of influence on ductility, impact resistance, or humanbody, the content of each of As and Sb is preferably lower than 0.05mass % and more preferably 0.02 mass % or lower. Further, Bi may bemixed in from a free-cutting copper alloy including Bi. In theembodiment, the Bi content is preferably 0.02 mass % or lower from aviewpoint of influence on human body and the environment.

The content of each of Mg, Ca, Zr, Ti, In, W, Mo, B, and rare earthelements as other elements is preferably lower than 0.05 mass %, morepreferably lower than 0.03 mass %, and still more preferably 0.02 mass %or lower.

The content of the rare earth elements refers to the total content ofone or more of the following elements: Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, and Lu.

Accordingly, the total content of these inevitable impurities ispreferably lower than 1.0 mass %, more preferably 0.7 mass % or lower,and still more preferably 0.5 mass % or lower.

(Composition Relational Expression f1)

The composition relational expression f1=[Cu]−4.5×[Si]+0.5×[Pb]−[P] isan expression indicating a relationship between the composition and themetallographic structure. Even when the amount of each of the elementsis in the above-described defined range, unless this compositionrelational expression f1 is not satisfied, the targeted properties ofthe embodiment cannot be obtained. When the composition relationalexpression f1 is lower than 56.5, the proportion of β phase increases,and ductility deteriorates. Accordingly, the lower limit of thecomposition relational expression f1 is 56.5 or higher, preferably 57.0or higher, and more preferably 57.2 or higher. As the compositionbecomes more preferable within the defined range of the compositionrelational expression f1, the proportion of α phase increases, excellentmachinability can be maintained, and good ductility, cold workability,impact resistance, and corrosion resistance can be obtained. Inparticular, when excellent cold workability is necessary, thecomposition relational expression f1 is still more preferably 57.5 orhigher.

On the other hand, the upper limit of the composition relationalexpression f1 affects the proportion of β phase or γ phase. When thecomposition relational expression f1 is higher than 59.5, the proportionof β phase decreases, and excellent machinability cannot be obtained. Atthe same time, the proportion of γ phase increases, ductility decreases,and strength also decreases. In some cases, μ phase also appears.Accordingly, the upper limit of the composition relational expression f1is 59.5 or lower, preferably 59.0 or lower, and more preferably 58.5 orlower. When particularly excellent machinability is required, the upperlimit of the composition relational expression f1 is preferably 58.3 orlower.

In addition, the composition relational expression f1 also deeplyrelates to hot workability performed at about 600° C. When thecomposition relational expression f1 is lower than 56.5, a problemoccurs in hot deformability. When the composition relational expressionf1 is higher than 59.5, hot deformation resistance increases, andprocessing at 600° C. becomes difficult to perform.

The free-cutting copper alloy according to the embodiment hasmachinability obtained by decreasing cutting resistance so that finelybroken chips are generated (for which a kind of brittleness is required)and ductility that are completely contradictory to each other. Bydiscussing not only the composition of each of the components but alsothe composition relational expression f1, the metallographic structurerelational expressions f2 to f6, and the metallographic structure andcomposition relational expression f6A in detail, an alloy more suitablefor the purpose and use can be provided.

Sn, Al, Fe, Mn, Co, Cr, and inevitable impurities that are separatelydefined are not defined by the composition relational expression f1because their influence on the composition relational expression f1 issmall if the content is within the range that can be considered asinevitable impurities.

(Comparison with Patent Documents)

Here, the results of comparison between the compositions of the Cu—Zn—Sialloys described in Patent Documents 2 to 15 and the composition of thealloy according to the embodiment are shown in Tables 1 and 2.

The embodiment and the alloys disclosed by Patent Documents 2 to 11 aredifferent from each other in the contents of Cu and Si, the mainelements of the alloys. In Patent Documents 2 to 11, a large amount ofCu is required.

In Patent Documents 2 to 4, 6, 9, and 11, β phase is depicted as ametallic phase that is not preferable in the metallographic because itimpairs machinability, and is treated as a phase having a negativeeffect in the relational expression regarding machinability. It is alsodisclosed that when β phase is present, it is preferable that β phase ischanged into γ phase having excellent machinability through a heattreatment.

In Patent Documents 4 and 9 to 11, in which an allowable amount of βphase is described, the maximum area ratio of β phase is 5% or lower.

In Patent Document 12, the content of each of Sn and Al is at least 0.1mass % or higher in order to improve dezincification corrosionresistance, and large amounts of Pb and Bi need to be included in orderto obtain excellent machinability.

Patent Document 13 describes a corrosion-resistant copper alloy castingwhich requires greater than or equal to 65 mass % Cu and has excellentmechanical characteristics and castability achieved by including Si anda small amount of Al, Sb, Sn, Mn, Ni, B, or the like.

Further, none of these Patent Documents disclose or imply the essentialrequirements of the embodiment, that are, β phase including Si hasexcellent machinability, 15% or more β phase is required at least, andthat compounds including fine P are present in β phase.

In Patent Document 15, greater than or equal to 0.2 mass % Sn isincluded, Sn and Si are included in order to improve dezincificationcorrosion resistance of β phase, hot extrusion is performed at atemperature of 700° C. or higher in order to improve machinability, anda heat treatment at 400° C. to 600° C. is required to improve corrosionresistance. The proportion of β phase is 5% to 25%, and the Si contentmay be 0.2 mass % or lower.

TABLE 1 Cu Si P Pb Sn Al Others First Embodiment 61.0-65.0 1.0-1.50.003-0.19  0.003-0.20 Sn + Al < 0.40 Fe + Mn + Cr + Co < 0.40 SecondEmbodiment 61.7-64.3 1.02-1.35 0.02-0.14 0.005-0.10 Sn + Al ≤ 0.30 Fe +Mn + Cr + Co ≤ 0.30 Patent Document 2 69-79 2.0-4.0 0.02-0.25 — 0.3-3.5 0.1-1.5 — Patent Document 3 69-79 2.0-4.0 0.02-0.25 0.02-0.4 0.3-3.5 0.1-1.5 — Patent Document 4 71.5-78.5 2.0-4.5 0.01-0.2  0.005-0.020.1-1.2  0.1-2.0 — Patent Document 5 69-88 2-5 0.01-0.25 0.004-0.450.1-2.5 0.02-1.5 Zr: 0.0005-0.04 Patent Document 6 69-88 2-5 0.01-0.250.005-0.45 0.05-1.5  0.02-1.5 Zr: 0.0005-0.04 Patent Document 774.5-76.5 3.0-3.5 0.04-0.10  0.01-0.25 0.05-0.2  0.05-0.2 Fe: 0.11-0.2Patent Document 8 70-83 1-5 0.1 or less — 0.01-2   — Fe, Co: 0.01-0.3Ni: 0.01-0.3 Mn: 0.01-0.3 Patent Document 9 73.0-79.5 2.5-4.0 0.015-0.2 0.003-0.25 0.03-1.0  0.03-1.5 — Patent Document 10 73.5-79.5 2.5-3.70.015-0.2  0.003-0.25 0.03-1.0  0.03-1.5 — Patent Document 11 75.4-78.03.05-3.55 0.05-0.13  0.005-0.070 0.05 or less 0.05 or less — PatentDocument 12 55-75 0.01-1.5  less than 0.15 0.01-4.0 0.1 or more 0.1 ormore — Patent Document 13 65-75 0.5-2.0 — — 0.01-0.55  0.1-1.0 — PatentDocument 14 — 0.25-3.0  — — — — — Patent Document 15 60.0-66.0 0.01-0.500.15 or less  0.05-0.50 0.20-0.90 — Fe: 0.60 or less

TABLE 2 Metallographic Structure First Embodiment 20 ≤ α ≤ 80, 15 ≤ β ≤80, 0 ≤ γ < 8 Second Embodiment 30 ≤ α ≤ 75, 25 ≤ β ≤ 70, 0 ≤ γ < 4Patent Document 2 γ phase, in some cases, κ phase is present. β phase isturned into γ phase by heat treatment. Patent Document 3 γ phase, insome cases, κ phase is present. β phase is turned into γ phase by heattreatment. Patent Document 4 18-500 Pb ≤ κ + γ + 0.3μ − β ≤ 56 + 500 Pb,0 ≤ β ≤ 5 Patent Document 5 α + κ + γ ≥ 80 Patent Document 6 α + γ + κ ≥85, 5 ≤ γ + κ + 0.3μ − β ≤ 95 Patent Document 7 — Patent Document 8 —Patent Document 9 30 ≤ α ≤ 84, 15 ≤ κ ≤ 68, β ≤ 3, etc. Patent Document10 60 ≤ α ≤ 84, 15 ≤ κ ≤ 40, β ≤ 2, etc. Patent Document 11 29 ≤ κ ≤ 60,β = 0, etc. κ phase is present in α phase. Patent Document 12 — PatentDocument 13 — Patent Document 14 — Patent Document 15 —

<Metallographic Structure>

In a Cu—Zn—Si alloy, 10 or more kinds of phases are present, acomplicated phase change occurs, and desired properties cannot benecessarily obtained simply by satisfying the composition ranges andrelational expressions of the elements. Eventually, by specifying anddetermining the kinds of metallic phases present in the metallographicstructure and the area ratio ranges thereof, desired properties can beobtained. Accordingly, the metallographic structure relationalexpressions are defined as follows.

20 ≤ f 2 = (α) ≤ 80 15 ≤ f 3 = (β) ≤ 800 ≤ f 4 = (γ) ≤ 8f5 = 18 × (γ)/(β) < 9 20 ≤ f 6 = (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) ≤ 8833 ≤ f 6A = (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) + ([Pb])^(1/2) × 35 + ([P])^(1/2) × 15

(γ Phase, Metallographic Structure Relational Expression f4)

As described in Patent Documents 2 to 6 and 9 to 11, γ phase is a phasethat contributes most to machinability in a Cu—Zn—Si alloy in which theCu concentration is about 69 mass % to 80 mass % and the Siconcentration is about 2 mass % to 4 mass %. In the embodiments also, γphase contributes to machinability. However, it is necessary to limit γphase in order to obtain a good balance between ductility and strength.Specifically, when the proportion of γ phase is 8% or higher, excellentductility or toughness cannot be obtained. Even when the amount of γphase is small, γ phase acts to improve chip breakability in drilling.However, as γ phase is a hard phase, when a large amount of γ phase ispresent, the thrust resistance value in drilling increases. Providingthat β phase is present at a proportion of 15% or higher, the effect ofγ phase on machinability corresponds to the value obtained by raisingthe amount of γ phase to the power of ½. When a small amount of γ phaseis included, γ phase has a large effect on improving machinability.However, when the amount of γ phase is further increased, the effect ofimproving machinability decreases. In consideration of ductility andcutting resistance in drilling and turning, the proportion of γ phaseneeds to be lower than 8%. The area ratio of γ phase is preferably 5% orlower and more preferably lower than 4%. When the area ratio of γ phaseis lower than 4%, the influence on ductility is reduced. However, whencold workability is required among others, it is preferable that thearea ratio of γ phase is lower than 1% or γ phase is not present. Thatis, even when (γ)=0, excellent machinability can be obtained by causingβ phase including Si to be present at a proportion described below.

(β phase, Metallographic Structure Relational Expressions f3 and f5)

In order to obtain excellent machinability with γ phase contained in anamount less than that described in the Patent Documents and almost no κphase or μ phase, it is important to optimize the Si content, theblending ratio between Cu and Zn, the amount of β phase, and the amountof Si solid-solubilized in β phase. Incidentally, it should be notedthat β phase includes β′ phase.

β phase in the composition range according to the embodiment has lowerductility than α phase, but has much higher ductility than γ phase or pphase, and also has higher ductility than κ phase. Accordingly, from aviewpoint of ductility, a relatively large amount of β phase can beincluded. On the other hand, γ phase has poor ductility and toughness.In addition, β phase can obtain excellent conductivity although itincludes high concentrations of Zn and Si. The amounts of β phase and γphase are significantly affected not only by the composition but also bythe process.

In a Cu—Zn—Si—P—Pb alloy, a free-cutting copper alloy according to theembodiment, it is necessary that the area ratio of β phase is at least15% or higher in order to obtain excellent machinability whileminimizing the Pb content, and also, the amount of β phase needs to bemore than twice the amount of γ phase in order to obtain excellentductility and high strength. That is, it is necessary to satisfyf5=18×(γ)/(β)<9 (which can be transformed to 2×(γ)<(β)). The amount of βphase is preferably 20% or higher and more preferably 25% or higher.Even when the amount of γ phase is lower than 4% (in some cases, 0%),excellent machinability can be obtained by satisfying the relationalexpressions f6 and f6A. When the amount of γ phase is lower than 4% andthe amount of β phase exceeds nine times the amount of γ phase,excellent ductility and toughness, and high strength can be obtained.The amount of β phase, then, is preferably 25% or higher, morepreferably 35% or higher, and still more preferably 40% or higher. Evenwhen the proportion of β phase is about 50% or about 40% and theproportion of α phase having poor machinability is about 50% or about60%, superb machinability of the alloy is maintained.

When the proportion of γ phase is 0% or lower than 1%, if the amount ofβ phase is about 50% or about 40% or higher, P-containing compounds arepresent and the machinability of a β single-phase alloy including Si ismaintained although depending on the Si concentration, the shape of αphase, and the distribution of β phase. It is presumed that soft α phasefunctions as a cushioning material around β phase and prevents α phasefrom causing an adverse effect not only on cutting resistance but alsoon chip breakability. Further, a phase boundary between hard β phase andsoft a phase functions as a stress concentration source of chipbreakage, and the chip breakability can be better than that of a singleβ-phase alloy depending on the shape of α phase. Further, when theamount of β phase is decreased to about 20%, the characteristics of αphase become predominant, and once the amount of β phase is decreased toabout 15% to about 25%, machinability rapidly deteriorates.

On the other hand, β phase has lower ductility than α phase. As theproportion of β phase decreases, ductility improves. In order to obtainexcellent ductility and a good balance between strength and ductility,the proportion of β phase is required to be 80% or lower, preferably 75%or lower, and more preferably 70% or lower. When ductility and coldworkability are important, the proportion of β phase is preferably 60%or lower and more preferably 50% or lower. The appropriate proportion ofβ phase slightly varies depending on the intended purpose of use andapplication.

β phase including about 1.5 mass % Si exhibits excellent hotdeformability and low hot deformation resistance when hot worked at alow hot working temperature of 500° C. or higher, and an alloy havingsuch β phase exhibits excellent hot deformability and low hotdeformation resistance.

(Si Concentration and Machinability of β Phase)

Regarding β phase, the more the Si content solid-solubilized in β phaseincreases within the composition range of the embodiment, the more themachinability improves. Therefore, the Si content in β phase ispreferably 1.2 mass % or higher. As a result of devoted study on therelationship between the Si concentration in the alloy, the amount of βphase, and the machinability of the alloy, it was revealed that, as aconvenient means, machinability of an alloy can be represented well bymultiplying the amount of β phase by the Si concentration (mass %, [Si])raised to the power of ½. That is, when two β phases are compared, onecontaining Si at a higher concentration has better machinability. Thatmeans, for example, an alloy whose Si concentration is 1.0 mass % needs1.1 times the amount of β phase contained in an alloy whose Siconcentration is 1.21 mass %. However, the machinability improvementeffect of β phase is saturated when the Si concentration in the alloy isin a range of about 1.35 mass % to about 1.5 mass %. Once the Siconcentration exceeds about 1.5 mass %, the higher the Si concentration,the worse the machinability of β phase. Regarding the Si content in βphase, when the Si content in β phase is higher than 1.9 mass %, themachinability of β phase deteriorates instead of improves. Thus, theamount of Si contained in β phase, that is, the amount of Sisolid-solubilized in β phase is preferably 1.2 mass % or higher and 1.9mass % or lower.

(β Phase, Metallographic Structure Relational Expression f6)

In addition to the metallographic structure relational expressions f3 tof5, the metallographic structure relational expression f6 defines theproportions of γ phase and β phase to obtain excellent machinability,ductility, and strength comprehensively by assigning coefficients to theproportions of γ phase and β phase, respectively. As described above, γphase exhibits excellent chip breakability during drilling even if itscontent is small, and a coefficient of 3 is multiplied by the amount(area %) of γ phase raised to the power of ½. β phase is expressed inthe metallographic structure relational expression f6, an expression toobtain machinability in which importance is put on the Si concentrationof the alloy, and the amount (area %) of β phase multiplied by the Siconcentration raised to the power of ½ and the value obtained bymultiplying the amount (area %) of γ phase raised to the power of ½ by acoefficient of 3 are added. The metallographic structure relationalexpression f6 is important, but is not effective unless the compositionrelational expression f1 and the metallographic structure relationalexpression f2 to f5 are satisfied. The lower limit value of themetallographic structure relational expression f6 for obtainingexcellent machinability is 20 or higher, preferably 30 or higher, andmore preferably 35 or higher. When machinability is important, the lowerlimit value of the metallographic structure relational expression f6 ispreferably 40 or higher and more preferably 45 or higher. On the otherhand, in consideration of properties such as ductility or strength, theupper limit of the metallographic structure relational expression f6 is88 or lower, preferably 82 or lower, and more preferably 77 or lower. Inparticular, when ductility and cold workability during cold rolling,slender bar production, or the like are important, the metallographicstructure relational expression f6 is preferably 67 or lower and morepreferably 60 or lower.

Incidentally, in the metallographic structure relational expressions f2to f6 and f6A, α phase, β phase, γ phase, δ phase, ε phase, ζ phase, ηphase, κ phase, μ phase, and χ phase are the subject metallic phases,and intermetallic compounds excluding P-containing compounds, Pbparticles, oxides, non-metallic inclusions, non-melted materials, andthe like are not the subjects. Most P-containing compounds are presentin β phase or at a boundary between α phase and β phase. Therefore, itis assumed that β phase includes the P-containing compounds that arepresent in β phase or at a boundary between α phase and β phase. Whenany P-containing compounds are present in a phase although it is rare,it is assumed that α phase includes the P-containing compounds.P-containing compound acts effectively in favor of machinability, andits content is small. Therefore, there is no problem to assume that βphase includes P-containing compounds. On the other hand, Intermetalliccompounds that are formed by Si or P and inevitably mixed-in elements(for example, Fe, Mn, Co, and Cr) are outside the scope of thecalculation of the area ratios of metallic phases.

(Metallographic Structure and Composition Relational Expression f6A)

As a conditional expression for an alloy to obtain excellentmachinability, it is necessary to add the effects of Pb and P forimproving machinability through distinctive actions to the expressionf6. When a very small amount of Pb is included under a condition whereP-containing compounds are present in β phase including Si,machinability improves. Likewise, as the amount of P solid-solubilizedin β phase increases, or as the amount of P-containing compoundsincreases, machinability improves. As a result of devoted study, it wasfound that the degree of improvement of machinability has a closerelationship with the values of the contents of Pb and P raised to thepower of ½. That is, even when the amount of Pb or P is tiny, theseelements exhibit a tremendous effect, and as the contents increase, theeffect of improving machinability increases. However, the degree of theimprovement gradually diminishes.

In summary, the Si concentration in β phase, the amount of β phase, theamount of P solid-solubilized in β phase, the amount of P-containingcompounds in β phase, and the content of Pb present as fine particlesimprove the machinability of the alloy through distinctive actionsrespectively. When all the requirements are satisfied, a large effect ofimproving machinability is exhibited due to the synergistic effect, andthe machinability of the alloy is significantly improved by including avery small amount of Pb or P.

In the metallographic structure and composition relational expressionf6A, a coefficient of 35 is multiplied by the value of the Pb content(mass %, [Pb]) raised to the power of ½, a coefficient of 15 ismultiplied by the value of the P content (mass %, [P]) raised to thepower of ½, and the obtained values are added to f6. In order to obtainexcellent machinability, f6A is at least 33 or higher, preferably 40 orhigher, more preferably 44 or higher, and still more preferably 50 orhigher. Even when the metallographic structure relational expression f6is satisfied, unless f6A in which the effects of Pb and P are added issatisfied, excellent machinability cannot be obtained. As long as thecontents of Pb and P are within the ranges defined by the embodiment,the effect on ductility or the like does not need to be defined by f6Asince it is defined by the upper limit of the relational expression f6.When the value of f6 is relatively low, the machinability is improved byincreasing the contents of Pb and P. Further, when machining conditionsare severe, for example, when machining is performed at a high cuttingspeed, when the feed rate is high, when the cutting depth in turning isdeep, or when holes with a large diameter are drilled, it is preferableto increase f6A, in particular, the value of the term related to Pb.

f6 and f6A are applied only within the concentration range of each ofthe elements defined by the embodiment and the ranges defined by f1 tof5.

(α Phase, Metallographic Structure Relational Expression f2, and Shapeof a phase)

α phase is a main phase forming the matrix together with β phase or γphase. α phase including Si has better machinability improvement effectthan α phase without Si, even though it is only by 5% to 10% in terms ofmachinability index. However, as the Si content increases, machinabilityimproves. In the case of a β single-phase alloy, there is a problem withthe ductility of the alloy, and an appropriate amount of a phase havinghigh ductility is required. Even when β phase having excellentmachinability and a phase having poor machinability are included, αphase itself functions as a cushioning material or as a stressconcentration source at a boundary with hard β phase during machining.Therefore, even when a relatively large amount of a phase is included,for example, about 50% in terms of area ratio, excellent machinabilitythat a β single-phase alloy has is maintained. As described above,machinability also depends on the Si concentration in the alloy, the Siconcentration in β phase, and the shape of a phase or how α phase isdistributed.

As a result of devoted study, in consideration of the ductility andtoughness of the alloy and the balance between ductility and strength,the amount of α phase is required to be 20% or higher, preferably 25% orhigher, and more preferably 30% or higher. When cold workability isimportant, for example, when cold drawing, cold wire-drawing, or coldrolling is performed at a high working ratio or when cold working suchas bending or crimping is performed, it is preferable that the arearatio of a phase is 40% or higher. On the other hand, in order to obtainexcellent machinability, the upper limit of the area ratio of a phase isat least 80% or lower, preferably 75% or lower, and more preferably 70%or lower or 65% or lower. In particular, when machinability isimportant, the area ratio of a phase is preferably 60% or lower.

(Machinability, Mechanical Characteristics, Shape of α Phase, andDistribution of β Phase)

Regarding the shape and distribution of α phase and the distribution ofβ phase that affect the machinability and/or the mechanicalcharacteristics of the alloy, when the shape of a phase crystal grainsis acicular (an elliptical shape in which the longer side/shorter sideratio of crystal grains is higher than 4), the dispersion of α phasedeteriorates, and acicular a phase having a large longer side hindersmachining. In addition, crystal grains of β phase around a phaseenlarge, and the state of dispersion of β phase also deteriorates.Further, the finer the α phase crystal grains are, the more themachinability and mechanical characteristics improve. The average sizeof α phase crystal grains is preferably 30 μm or less. When α phasecrystal grains are granular and fine, a phase is uniformly distributed,causing β phase to be divided. Therefore, in terms of machinability,strength, and ductility, α phase functions as a good cushioningmaterial, or a phase boundary between a phase and β phase functions as astress concentration source for chip breakage, and chips are more likelyto be broken than those of a β single-phase alloy. Accordingly, as apreferred embodiment, when the proportion of α phase crystal grainshaving a longer side/shorter side ratio of 4 or lower in the entirety ofα phase ((the number of granular α phase crystal grains whose “longerside/shorter side” ratio is 4 or lower/the total number of α phasecrystal grains)×100) is 50% or higher and preferably 75% or higher,machinability improves. When the proportion of acicular a phase crystalgrains having a large longer side exceeds 50%, about the same level ofductility is maintained, but the strength of the alloy decreases.Accordingly, when the proportion of granular α phase crystal grainsincreases, the strength increases, and the balance between strength andductility improves. Regarding the shape of α phase crystal grains,whether or not the proportion of the acicular or elliptical α phasecrystal grains whose “longer side/shorter side” ratio is higher than 4exceeds 50% or 25% is affected by the production process. When the hotworking temperature increases, the proportion of acicular or ellipticala phase crystal grains whose “longer side/shorter side” ratio is higherthan 4 increases.

(μ Phase, κ Phase, and Other Phases)

In order to obtain high ductility or toughness, and high strengthtogether with excellent machinability, presence of the phases other thanα, β, and γ phases is also important. In the embodiment, considering theproperties of the alloy, κ phase, μ phase, δ phase, ε phase, ζ phase, orη phase is not particularly required. When the sum of the constituentphases (α), (β), (γ), (μ), (κ), (δ), (ε), (ζ), and (η) that form themetallographic structure is represented by 100, it is preferable that(α)+(β)+(γ)>99, and it is most preferable that (α)+(β)+(γ)=100 providingthat calculation error and number rounding are disregarded.

(Presence of P-Containing Compounds)

In β phase including Si, chip breakability is insufficient as comparedto a free-cutting copper alloy including 3 mass % Pb, and the cuttingresistance in turning and the torque in drilling are high. Byprecipitating P-containing compounds having an average particle size ofabout 0.5 to 3 μm in β phase, the machinability of β phase can befurther improved. Simply speaking, the effect of improving machinabilityobtained by the presence of P-containing compounds corresponds to animprovement of about 10%, in some cases, about 12% in terms ofmachinability index. Machinability is also affected by the P content,the amount and distribution of β phase, as well as the size,distribution state, etc. of the P-containing compounds to be formed.P-containing compound is a compound including P and at least either orboth of Si and Zn. In some cases, it can further includes Cu and/orinevitable impurities such as Fe, Mn, Cr, or Co. P-containing compoundsare affected by inevitable impurities such as Fe, Mn, Cr, and Co, too.When the concentration of the inevitable impurities exceeds theafore-mentioned defined amount, the composition of P-containing compoundchanges such that P-containing compound may no longer contribute toimprovement of machinability. Incidentally, P-containing compounds arenot present at a hot working temperature of about 600° C. They areproduced at a critical cooling rate during cooling after hot working.Accordingly, the cooling rate after hot working is important, and it ispreferable that cooling is performed at an average cooling rate of 50°C./min or lower in a temperature range from 530° C. to 450° C. Thisaverage cooling rate is more preferably 45° C./min or lower. On theother hand, when the cooling rate is excessively slow, P-containingcompounds are likely to grow bigger, which causes the effect onmachinability to decrease. The lower limit of the average cooling rateis preferably 0.1° C./min or higher and more preferably 0.3° C./min orhigher.

Now, FIGS. 1A to 1C show metallographic structure images of variousalloys.

The copper alloy shown in FIG. 1A is an alloy comprising 62.9 mass % Cu,1.14 mass % Si, 0.072 mass % P, 0.009 mass % Pb, and Zn as the balance,which is obtained by hot extrusion at 590° C. and an average coolingrate of 25° C./min in a temperature range from 530° C. to 450° C.

The copper alloy shown in FIG. 1B is an alloy comprising 62.9 mass % Cu,1.14 mass % Si, 0.072 mass % P, 0.009 mass % Pb, and Zn as the balance,which is obtained by hot forging at 615° C. and an average cooling rateof 28° C./min in a temperature range from 530° C. to 450° C.

The copper alloy shown in FIG. 1C is an alloy comprising 62.5 mass % Cu,1.05 mass % Si, 0.001 mass % P, 0.016 mass % Pb, and Zn as the balance,which is obtained by hot extrusion at 595° C. and an average coolingrate of 25° C./min in a temperature range from 530° C. to 450° C.

As shown in FIGS. 1A and 1B, when the hot extruded material and the hotforged material are observed with a metallographic microscope, granularprecipitates having a particle size of about 0.5 to 3 μm that look blackare present in β phase and at a phase boundary between β phase and αphase. In addition, in most of a phase crystal grains, the longerside/shorter side is 4 or lower, and the average size of α phase crystalgrains is about 15 μm in FIG. 1A and is about 25 μm in FIG. 1B.

On the other hand, in FIG. 1C, the P content is 0.001 mass %. Therefore,no precipitate including P is present. In a comparison between FIG. 1Cand FIGS. 1A and 1B, even if etching is performed under the samecondition, when the P content is 0.001 mass % (FIG. 1C), phaseboundaries between α phase and β phase are not clear. However, when theP content is 0.072 mass % (FIGS. 1A and 1B), phase boundaries between αphase and β phase look clearer. That the P content of the former is0.001 mass % and the difference of 0.071 mass % in the P content hascaused the metallographic structure to changed.

(Si Content Solid-Solubilized in β Phase and Machinability)

The contents of Cu, Zn, and Si in α phase, β phase, and γ phase formedin the composition range of the embodiment roughly have the followingrelationships.

The Cu concentration: α>β≥γ.

The Zn concentration: β>γ>α.

The Si concentration: γ>β>α.

Regarding a sample (an alloy including 64.1 mass % Cu, 1.21 mass % Si,0.035 mass % P, and Zn as the balance) that was hot-extruded to φ25.4 mmat 590° C. on the actual production line, a sample (an alloy including62.9 mass % Cu, 1.14 mass % Si, 0.07 mass % P, and Zn as the balance)that was heat-treated at 410° C. for 50 minutes on the actual productionline, and samples (an alloy including 64.0 mass % Cu, 1.31 mass % Si,0.05 mass % P, and Zn as the balance and an alloy including 62.3 mass %Cu, 1.06 mass % Si, 0.04 mass % P, and Zn as the balance) that wereextruded to φ22 mm at 595° C. in a laboratory, the concentrations of Cu,Zn, and Si in α, β, and γ phases were quantitatively analyzed with anX-ray microanalyzer using secondary electron images and compositionalimages of the samples taken at a magnification of 2000-fold. Themeasurement was performed using “JXA-8230” (manufactured by JEOL Ltd.)under the conditions of acceleration voltage: 20 kV and current value:3.0×10⁻⁸ A. The results are shown in Tables 3 to 6.

The concentration of the Si solid-solubilized in β phase is about 1.5times that in α phase. That is, about 1.5 times the amount of Si in αphase is distributed in β phase. For example, when the Si concentrationin the alloy is 1.2 mass %, about 1.0 mass % Si is solid-solubilized ina phase, and 1.5 mass % Si is solid-solubilized in β phase.

An alloy having a representative composition of Patent Document 2, thatis, 76 mass % Cu, 3.1 mass % Si, and Zn as the balance, was prepared andanalyzed with an X-ray microanalyzer (EPMA). The result was that thecomposition of γ phase was 73 mass % Cu, 6 mass % Si, and 20.5 mass %Zn. This composition of γ phase is significantly different from thecomposition of 60.5 mass % Cu, 3.5 mass % Si, and 36 mass % Zn, which isa composition example of γ phase in the embodiment, and therefore, it isexpected that characteristics of the γ phases of the alloys are alsodifferent.

TABLE 3 Alloy of Zn-64.1 mass % Cu-1.21 mass % Si -0.035 mass % P Cu ZnSi α phase 66.0 32.5 1.0 β phase 61.0 37.5 1.5 γ phase 60.5 36.0 3.5

TABLE 4 Alloy of Zn-62.9 mass % Cu-1.14 mass % Si -0.07 mass % P Cu ZnSi α phase 65.5 33.5 0.9 β phase 60.5 38.0 1.4

TABLE 5 Alloy of Zn-64.0 mass % Cu-1.31 mass % Si -0.05 mass % P Cu ZnSi α phase 66.0 32.5 1.1 β phase 61.0 37.0 1.6 γ phase 60.5 35.5 3.7

TABLE 6 Alloy of Zn-62.3 mass % Cu-1.06 mass % Si-0.04 mass % P Cu Zn Siα phase 65.0 34.0 0.9 β phase 60.0 38.5 1.3

(Machinability Index)

In general, machinability of various copper alloys is expressed bynumerical value (%) by comparison with a free-cutting brass including 3mass % Pb which is used as a standard, i.e., 100% refers to themachinability of the standard alloy. Machinability of copper alloys isdescribed, for example, in “Basic and Industrial Technique of Copper andCopper Alloy (Revised Edition)” (1994, Japan Copper and BrassAssociation), p. 533, Table 1, and Metals Handbook TENTH EDITION Volume2 Properties and Selection: Nonferrous Alloys and Special-PurposeMaterials” (1990, ASM International), p. 217 to 228.

Alloys in Table 7 are alloys including 0.01 mass % Pb prepared in alaboratory as described below by hot-extruding to φ22 mm using anextrusion test machine in the laboratory. In the case of Cu—Zn binaryalloys, containing a small amount of Pb hardly affects the machinabilityof the alloy. Therefore, 0.01 mass % Pb, which falls within thecomponent range of the embodiment, was added to each of the alloys. Thehot extrusion temperature of Alloys A and D was 750° C., and the hotextrusion temperature of the other alloys, Alloys B, C, E, and F, was635° C. After the extrusion, a heat treatment was performed at 500° C.for 2 hours to adjust the metallographic structure. The turning anddrilling tests described below were performed to find out themachinability of the alloys. A commercially available free-cuttingbrass, C3604 (comprising 59 mass % Cu, 3 mass % Pb, 0.2 mass % Fe, 0.3mass % Sn, and Zn as the balance) was used as the standard free-cuttingbrass material.

TABLE 7 Metallographic Component Composition Structure (%) Material CuZn Si Pb P α β Alloy A α brass 65.0 35.0 0 0.01 0 100 0 Alloy B 50% β58.1 41.9 0 0.01 0 52 48 brass Alloy C β brass 54.0 46.0 0 0.01 0 0 100Alloy D α brass 69.1 30.0 0.88 0.01 0 100 0 with 0.9 Si Alloy E β brass59.8 38.8 1.30 0.01 0 0 100 with 1.3 Si Alloy F β brass 59.6 39.0 1.300.01 0.05 0 100 with P + 1.3 Si

TABLE 8 Machin- Turning Hole Drilling ability Cutting Cutting ResistanceOverall Resistance Overall Torque Thrust (%) (%) Chips (%) (%) (%) ChipsAlloy 31 33 X 28 26 30 X A Alloy 44 39 X 49 46 52 X B Alloy 51 41 X 6153 68 X C Alloy 38 39 X 36 33 39 X D Alloy 75 79 Δ 71 65 76 Δ E Alloy 8593 ◯ 76 74 77 ◯ F

The above-mentioned Patent Documents describe that the machinability ofa 70 Cu-30 Zn alloy which is an a single-phase brass is 30%. In theembodiment, as shown in Tables 7 and 8, the machinability of a 65 Cu-35Zn alloy (Alloy A), which is also an a single-phase brass, was 31%. Inthe α single-phase brass in which the contents of Cu and Zn wereadjusted and the Si content was 0.9 mass % (Alloy D), that is, an asingle-phase brass in which 0.9 mass % Si was solid-solubilized in aphase, the machinability index was improved by about 7% compared with ana brass not including Si. Chips of Alloys A and D generated in theturning and drilling tests were both continuous.

The force of turning can be decomposed into a principal cutting force, afeed force, and a thrust force, but the combined force (three forcecomponents) thereof was regarded as the cutting resistance. In the caseof drilling, the force was decomposed into torque and thrust, and theaverage value thereof is described as “Overall” cutting resistance ofdrilling. Further, as the machinability of the alloy, the cuttingresistance during turning and that during drilling were averaged, andthe average value was described as the “Overall” machinability index(evaluation).

In a β single-phase brass in which the contents of Cu and Zn wereadjusted and Si was not included (Alloy C, 54 Cu-46 Zn), the “overall”machinability index improved about 20% compared with an a phase brassnot including Si. Yet, with the “overall” machinability index stillstanding at 51%, there was little improvement in chips, and the chipevaluation remained the same. In a β single-phase alloy including about1.3 mass % Si (Alloy E), the “overall” machinability index furtherimproved 24% compared with a β single-phase alloy not including Si(Alloy C). Chips generated during turning and drilling were slightlyimproved and were broken, but the difference from those of afree-cutting brass including 3 mass % Pb was large.

In a β single-phase alloy including 0.05 mass % P and 1.3 mass % Si(Alloy F), the “overall” machinability index was improved by about 10%compared with a β single-phase alloy including 1.3 mass % Si withoutincluding P. Due to inclusion of P, the turning performance improvedabout 14%, and the torque in drilling remarkably improved about 9%. Themagnitude of cutting resistance in turning and that of torque indrilling are related to chip shape, and by including 0.05 mass % P, theevaluation result of the chip shape improved from “Δ” to “◯”. Thedifference with a free-cutting brass including 3% Pb in the resistanceduring turning narrowed, and chips produced during turning and drillingsignificantly improved having substantially the same shape as those of afree-cutting brass including 3% Pb. Incidentally, cutting resistance ofan alloy is affected by its strength. When hot extruded materials arecompared to each other, the higher the strength, the higher the cuttingresistance. β single-phase brass and the alloy according to theembodiment have a strength that is 1.2 to 1.3 times that of afree-cutting brass including 3 mass % Pb. If the difference is takeninto consideration, it can be said that the machinability of a βsingle-phase alloy including 1.3 mass % Si and 0.05 mass % P issubstantially equivalent to the machinability of a free-cutting brassincluding 3 mass % Pb.

According to Tables 4 and 6, Alloy F, a β single-phase alloy,corresponds to β phase of the free-cutting copper alloy according to theembodiment, and Alloy D corresponds to a phase thereof. The free-cuttingcopper alloy according to the embodiment is composed of β phase havingmachinability substantially comparable to that of a free-cutting brassincluding 3 mass % Pb (Alloy F) and a phase in which the machinabilityis improved by including Si (Alloy D). In the free-cutting copper alloyaccording to the embodiment, even when the proportion of β phase isreduced to about 50% or about 40%, the machinability of Alloy F, a βsingle-phase alloy, which is comparable to that of a leaded free-cuttingbrass, can be substantially maintained.

On the other hand, Alloy B is a brass including 0.01 mass % Pb and notincluding Si or P, in which the proportion of β phase is 48%, and thecutting resistances in turning and drilling improved surpassing that ofan α single-phase brass (Alloy A). However, the cutting resistance washigher than that of a β single-phase brass (Alloy C), and the “overall”machinability evaluation was 44%, which is 35% points lower than that ofthe alloy according to the embodiment of the present invention havingthe same proportion of β phase, and the chip shapes were totallydifferent from each other. There is no way that a brass including 0.01mass % Pb, not including Si or P, and including 48% β phase can be areplacement of a free-cutting brass including 3 mass % Pb from aperspective of cutting resistance and chip shape.

The free-cutting copper alloy according to the embodiment includesP-containing compounds in β phase, and has good machinability due to theeffect of 1.3% to 1.6 mass % Si contained in β phase as shown in Tables3 to 6.

<Properties>

(Normal-Temperature Strength and High Temperature Properties)

There is a strong demand for reduction in the thickness and weight ofparts and components that are target applications of the embodiment suchas auto parts. Among the strengths that are required, tensile strengthis important, and the balance between tensile strength and ductility isalso important.

In this regard, it is preferable that hot extruded materials, hot rolledmaterials, and hot forged materials are high strength materials having atensile strength of 470 N/mm² or higher in a state where cold working isnot performed after hot working. The tensile strength is more preferably500 N/mm² or higher and still more preferably 530 N/mm² or higher. Manycomponents that are used for valves, joints, pressure vessels, airconditioners, or freezers are manufactured by hot forging. A leadedcopper alloy currently used has a tensile strength of about 400 N/mm²and an elongation of 30% to 35%. Therefore, a reduction in weight can berealized by increasing the strength.

Cold working may also be performed after hot working, and a materialthat falls within the following range is defined as a high-strength andhigh-ductility material in consideration of the influence of coldworking.

A hot worked material, a material that is further cold-worked at aworking ratio of 30% or lower after hot working, or further cold-workedand heat-treated after hot working, then cold-worked to a working ratioof 30% or lower have the following properties. Hereinafter, the finalcold working ratio is represented by [R]%, and when cold working is notperformed, [R]=0. The tensile strength S (N/mm²) is (470+8×[R]) N/mm² orhigher and preferably (500+8×[R]) N/mm² or higher. The elongation E (%)is (0.02×[R]²−1.15×[R]+18)% or higher, and preferably(0.02×[R]²−1.2×[R]+20)% or higher. The characteristic relationalexpression f7=S×(100+E)/100 indicating the balance between strength andductility is preferably 600 or higher, more preferably 640 or higher,still more preferably 670 or higher, and most preferably 700 or higher.

Incidentally, in a hot-worked, free-cutting brass including Pb on whichno further working is performed after hot-working, the characteristicrelational expression f7 is about 530. The characteristic relationalexpression f7 of the copper alloy according to the embodiment is higherthan this by at least 70, possibly 100 or higher, indicating that thebalance between strength and ductility is excellent.

(Electrical Conductivity)

The applications of the embodiment include electrical and electronicapparatus components, components of automobiles in the field whereelectrification is in progress, and other parts and components havinghigh conductivity. Currently, phosphor bronzes including 6 mass % or 8mass % Sn (JIS standards, C5191, C5210) are widely used for theseapplications, and their electrical conductivities are about 14% IACS and12% IACS, respectively. Accordingly, no serious problem related toelectric conductivity occurs to the copper alloy according to theembodiment as long as it has an electrical conductivity of 13% IACS orhigher. The electrical conductivity is preferably 14% IACS or higher.The reason that the copper alloy according to the embodiment exhibitshigh conductivity despite inclusion of elements that deteriorateelectrical conductivity, specifically, Si in an amount exceeding 1 mass% and Zn in an amount about 33 mass % or higher, is the influence of theamount of β phase in the alloy and Si solid-solubilized in β phase. Theupper limit of the electrical conductivity is not particularly definedbecause an increase in conductivity rarely causes a problem in practice.

From the above-stated results of study, the following findings wereobtained.

First, in the conventional art, it was known that β phase formed in aCu—Zn—Si alloy has no effect on machinability of an alloy or has anegative effect on the machinability. However, as a result of devotedstudy, it was found that β phase comprising, for example, about 1.5 mass% Si, about 61 mass % Cu, and about 37.5 mass % Zn has extremely goodmachinability.

Second, it was found that, if β phase is made to contain P such that Pis solid-solubilized in β phase and P-containing compounds having anaverage particle size of about 0.5 to about 3 μm are made to precipitatein β phase for the purpose of further improving the machinability of βphase in a Cu—Zn—Si alloy, the cutting resistance further decreases, andthe chip breakability significantly improves compared with an alloy notincluding P or in which no P-containing compounds are present.

Third, it was found that γ phase formed in the free-cutting copper alloyaccording to the embodiment has an effect to obtain excellent chipbreakability. The copper alloys of the Patent Documents havecompositions different than that of the free-cutting copper alloyaccording to the embodiment. Even though the copper alloys of the PatentDocuments and the free-cutting copper alloy according to the embodimentboth have γ phase, if the composition is different, there is a largedifference in machinability similarly to β phase as described above.And, it was found that γ phase present within the composition range ofthe embodiment also has excellent machinability. It was revealed that inthe embodiment, although the Cu content and the Si content are low, themachinability, in particular, chip breakability of γ phase duringdrilling, is excellent. However, since γ phase impairs ductility, it wasnecessary to limit its amount. It was found that, in the metallographicstructure comprising two phases of a phase and β phase without includingγ phase (for the purpose of prioritizing the ductility of the alloy),machinability is excellent.

Fourth, β phase including about 1.5 mass % Si has high strength but itsductility is poor. An alloy containing an excessive amount of β phase isnot suitable as an industrial material. The free-cutting copper alloyaccording to the embodiment was completed by optimizing the respectiveparameters including the amount of a phase, the amount of β phase, theamount of γ phase, the size of a phase crystal grains (crystal grainsize of a phase), and the shape of α phase crystal grains for thepurpose of maintaining machinability such as excellent chip breakabilityand low cutting resistance.

Fifth, it was revealed that, when a small amount of Pb is contained in acopper alloy whose machining performance has been improved by includingβ phase in which Si is contained and P-containing compounds are present,such Pb exhibits an effect of improving chip breakability and reducingcutting resistance. The alloy according to the embodiment was completedby finding out not only the previously described P content but also theeffect of the Pb content on machinability and obtaining a furtheroptimized composition and metallographic structure in consideration ofmachinability, other properties, and influence on human body.

Sixth, conventional leaded copper alloys had a problem in hotdeformability at 650° C. or lower because they contain a large amount ofPb which is in a molten state at a hot working temperature. The alloyaccording to the embodiment was completed as a copper alloy having goodductility during hot working, excellent hot deformability at about 600°C., a temperature lower than 650° C., low hot deformation resistance,which can be hot worked easily.

(Hot Workability)

The free-cutting copper alloy according to the embodiment has acharacteristic that it has excellent deformability at about 600° C., canbe hot-extruded into a bar having a small cross-sectional area, and canbe hot-forged into a complex shape. When high deformation is performedon a leaded copper alloy at about 600° C., a large crack is formed.Therefore, the appropriate hot extrusion temperature is 625° C. to 800°C., and the appropriate hot forging temperature is 650° C. to 775° C.The free-cutting copper alloy according to the embodiment has acharacteristic that it does not crack when hot working is performed at aworking ratio of 80% or higher at 600° C. A preferable hot workingtemperature for the free-cutting copper alloy according to theembodiment is a temperature lower than 650° C. and more preferably lowerthan 625° C.

In the free-cutting copper alloy according to the embodiment, hotdeformability of α phase and β phase is improved and deformationresistance is reduced at 600° C. due to inclusion of Si. Since theproportion of β phase is high, hot working can be easily performed at600° C.

When the hot working temperature is about 600° C. which is lower thanthe working temperature of conventional copper alloys, tools such as anextrusion die for hot extrusion, containers of extruder, and metal moldsfor forging are heated to 400° C. to 500° C. and used. The smaller thedifference in temperature between the tools and the hot worked material,the more homogeneous the metallographic structure, the better thedimensional accuracy of a hot worked material, and the longer the toollife because tool temperature does not substantially increase. Inaddition, a material having a high strength and a good balance betweenstrength and elongation can be obtained.

<Production Process>

Next, a method for producing the free-cutting copper alloys according tothe first and second embodiments of the present invention will bedescribed.

The metallographic structure of the alloy according to the embodimentvaries not only depending on the composition but also depending on theproduction process. The metallographic structure of the alloy isaffected not only by hot working temperatures in hot extrusion and hotforging and heat treatment conditions but also by the average coolingrate in the process of cooling after hot working or heat treatment. As aresult of a devoted study, it was found that the metallographicstructure is significantly affected by the cooling rate in a temperaturerange from 530° C. to 450° C. in the process of cooling after hotworking or heat treatment.

(Melting and Casting)

Melting is performed at about 950° C. to about 1200° C., a temperaturethat is about 100° C. to about 300° C. higher than the melting point(liquidus temperature) of the alloy according to the embodiment. Amolten alloy having a temperature of about 900° C. to about 1100° C., atemperature that is about 50° C. to about 200° C. higher than themelting point is cast into a predetermined mold and is cooled by somecooling means such as air cooling, slow cooling, or water cooling. Afterthe alloy solidifies, constituent phases change in various ways.

(Hot Working)

Examples of hot working include hot extrusion, hot forging, and hotrolling. When two or more hot working steps are performed, the final hotworking step is performed under the following condition.

First, regarding hot extrusion, in a preferred embodiment, althoughdepending on extrusion ratio (hot working ratio) and facility capacity,hot extrusion is performed such that the material's temperature when itis being hot worked, specifically, immediately after the material passesthrough the extrusion die (hot working temperature) is higher than 540°C. and lower than 650° C. The lower limit of the hot extrusiontemperature relates to hot deformation resistance, and the upper limitthereof relates to the shape of α phase. By controlling the hotextrusion temperature such that it is within a narrower temperaturerange, a stable metallographic structure can be obtained. When hotextrusion is performed at 650° C. or higher, the shape of α phasecrystal grains is likely to be acicular instead of granular, or large αphase crystal grains having a diameter of more than 50 μm are likely toappear. When acicular and large α phase crystal grains appear, thestrength slightly decreases, the balance between strength and ductilityslightly deteriorates, the distribution of P-containing precipitatesslightly deteriorates, and the machinability slightly deteriorates aslarge a phase crystal grains having a large longer side hindermachining. The shape of α phase crystal grains relates to thecomposition relational expression f1, and when the compositionrelational expression f1 is 58.0 or lower, the extrusion temperature ispreferably lower than 625° C. By performing extrusion at a temperaturelower than the temperature at which common copper alloys are extruded,good machinability and strength can be obtained.

Further, by adjusting the cooling rate after hot extrusion, that is, byperforming cooling in a temperature range from 530° C. to 450° C. in theprocess of cooling after hot extrusion at an average cooling rate of 50°C./min or lower and preferably 45° C./min or lower, a material havingbetter machinability can be obtained. By limiting the average coolingrate to 50° C./min or lower, the presence of P-containing compounds canbe observed with a metallographic microscope at a magnification of500-fold. On the other hand, if the cooling rate is excessively slow,P-containing compounds are likely to grow bigger, and the effect onmachinability may decrease. Therefore, the average cooling rate ispreferably 0.1° C./min or higher and more preferably 0.3° C./min orhigher.

From a perspective of practicability of measurement position, hotworking temperature is defined as a temperature of a hot worked materialat which measurement can be performed about three or four seconds afterhot extrusion, hot forging, or hot rolling is completed. Themetallographic structure is affected by the temperature immediatelyafter working where large plastic deformation occurs. The averagecooling rate after hot working in question is about 50° C./min.Therefore, a temperature decrease during the 3 to 4 seconds after hotworking is calculated to be about 3° C., and thus there is littleinfluence.

As a material for hot forging, a hot extruded material is mainly used,but a continuously cast bar is also used. Compared with hot extrusion,in hot forging, the working rate is higher, and a more complex shape isformed. In some cases, high deformation can be performed up to athickness of about 3 mm, and thus the forging temperature is higher thanthe hot extrusion temperature. In a preferred embodiment, thetemperature of a hot forged material on which plastic working isperformed to form a main portion of a forged product, that is, thematerial's temperature about three or four seconds immediately afterforging (after completion of forging) is preferably higher than 540° C.and lower than 675° C. In a brass alloy including 2 mass % Pb that iswidely used as a brass alloy for forging (59Cu-2Pb-balance Zn), thelower limit of the hot forging temperature is 650° C. Hot forgingtemperature of the embodiment is more preferably lower than 650° C. Hotforging relates to the composition relational expression f1, and whenthe composition relational expression f1 is 58.0 or lower, the hotforging temperature is preferably lower than 650° C. Although dependingon the working ratio in hot forging, the lower the temperature, thesmaller the size of α phase crystal grains, the more likely the shape ofα phase crystal grains change from an acicular shape into a granularshape, the higher the strength, the more the balance between strengthand ductility improves, and the more the machinability improves.

By adjusting the cooling rate after hot forging, a material havingvarious characteristics of machinability can be obtained. That is,cooling is performed after hot forging with the average cooling rate ina temperature range from 530° C. to 450° C. set at 50° C./min or lowerand preferably 45° C./min or lower. By controlling the cooling rate suchthat compounds including mainly P and Si having a particle size of about0.5 to 3 μm and Zn precipitate in β phase or at a boundary between βphase and a phase where phase change occurs, the machinability of thealloy can be further improved. Incidentally, when the cooling rate isexcessively slow, the compounds enlarge in the process of cooling.Therefore, the lower limit of the above-mentioned average cooling rateis 0.1° C./min or higher and preferably 0.3° C./min or higher.

In hot rolling, an ingot is heated and rolled 5 to 15 times repeatedly.The material's temperature upon completion of the final hot rolling (thematerial's temperature three or four seconds after completion of theprocess) is preferably higher than 540° C. and lower than 650° C., andmore preferably lower than 625° C. After completion of hot rolling, therolled material is cooled. In this cooling, as in hot extrusion, theaverage cooling rate in a temperature range from 530° C. to 450° C. ispreferably 0.1° C./min or higher and 50° C./min or lower. Theabove-mentioned average cooling rate is more preferably 0.3° C./min orhigher or 45° C./min or lower.

(Heat Treatment)

A main heat treatment of the copper alloy is also called annealing. Heattreatment is performed as necessary. For example, when making a smallproduct which cannot be produced by hot extrusion, heat treatment isperformed after cold-drawing or cold wire-drawing for the purpose ofrecrystallization, that is, to soften the material. Likewise, rolledmaterial is cold-rolled and heat-treated. In the embodiment, a heattreatment is also performed in order to control the amounts of γ phaseand β phase.

When a heat treatment to induce recrystallization is required, thematerial is heated to a temperature of 400° C. or higher and 600° C. orlower for 0.1 to 8 hours. When P-containing compounds are not formed inthe previous step, they are formed during heat treatment. When heattreatment is performed at a temperature of higher than 530° C.,P-containing compounds are solid-solubilized again and disappear. Whenthe heat treatment temperature is higher than 530° C., it is necessaryto perform the cooling with the average cooling rate in a temperaturerange from 530° C. to 450° C. in the process of cooling set to be 50°C./min or lower and preferably 45° C./min or lower such thatP-containing compounds are formed. The lower limit of the averagecooling rate is preferably 0.1° C./min or higher.

(Cold Working Step)

In the case of a hot extruded bar, cold working may be performed on ahot extruded material in order to obtain a high strength, to improve thedimensional accuracy, or to straighten (reduce the degree of bending of)an extruded bar or a coiled material. For example, cold-drawing at aworking ratio of about 2% to about 30% is performed on a hot extrudedmaterial, and optionally straightness correction and low-temperatureannealing are performed after cold-drawing.

If the material is a slender bar, a wire, or a rolled material, coldworking and a heat treatment are repeatedly performed. After the heattreatment, cold working, straightness correction, and/or low-temperatureannealing are performed such that the final working ratio becomes 0% toabout 30%.

An advantage of cold working is that the strength of the alloy can beincreased by the process. By performing a combination of cold workingand heat treatment on a hot worked material, no matter which step isperformed first, high strength, ductility, and impact resistance can bewell-balanced, and properties demanded by the respective applications inwhich strength, ductility, and/or toughness are considered important canbe obtained. The influence of cold working on machinability is limited.

(Low-Temperature Annealing)

In the case of bars, wires, forged products, and rolled materials, forthe main purposes of removal of residual stress, correction of a bar(straightness of a bar), and adjustment and improvement of themetallographic structure, low-temperature annealing is sometimesperformed at a temperature equal to or lower than the recrystallizationtemperature in the final step. In the case of the embodiment, in orderto distinguish low-temperature annealing from the above-described heattreatment, low-temperature annealing is defined to be a process whichinduces recrystallization where the recrystallized portion in themetallographic structure is lower than 50%. Low-temperature annealing isperformed with a holding temperature of 250° C. or higher and 430° C. orlower and a holding time of 10 minutes to 200 minutes. The lower limitsof temperature and time are those where residual stress can besufficiently removed. In addition, bars with excellent straightness canbe obtained by arranging bars in a mold whose cross-section has a recessand the bottom surface is smooth and flat, for example, a steel moldhaving a width of about 500 mm, a height of about 300 mm, a thickness ofabout 10 mm, and a length of about 4000 mm (the depth of the recessrefers to (height)−(thickness)), and holding the bars at a temperatureof 250° C. or higher and 430° C. or lower for 10 minutes to 200 minutes.When the temperature is represented by T° C. and the time is representedby t min, it is preferable that 300≤annealing conditional expressionf8=(T−200)×(t)^(1/2)≤2000. When annealing conditional expression f8 islower than 300, the removal of residual stress or straightnesscorrection is insufficient. When the annealing conditional expression f8is higher than 2000, the strength of the material decreases due torecrystallization. The annealing conditional expression f8 is preferably400 or higher and 1600 or lower. Irrespective of the cooling rate in theprevious step, when the annealing conditional expression f8 is 400 orhigher, compounds including fine P are formed during low-temperatureannealing. In addition, although depending on the alloy's composition,when a material is held at a temperature of 250° C. or higher and 430°C. or lower for 10 minutes to 200 minutes, fine γ phase can beprecipitated in β phase and at a phase boundary between β phase and αphase, making the chips generated by drilling become fine. However,machinability may deteriorate since the amount of β phase decreases asthe amount of γ phase increases. In addition, when the amount of γ phaseis excessively large, the improvement of machinability is saturated,which causes ductility to deteriorate. Therefore, it is necessary to payattention to the metallographic structure relational expressions f2 tof6.

Using the above-mentioned production method, the high-strengthfree-cutting copper alloy according to the first and second embodimentsof the present invention are produced.

The hot working step, the heat treatment (also referred to as“annealing”) step, and the low-temperature annealing step are steps ofheating the copper alloy. Basic production steps are melt and casting,hot working (extrusion, forging, rolling), cold working (wire-drawing,drawing, rolling), straightness correction, and low-temperatureannealing, but straightness correction, cold working, or low-temperatureannealing may not be included. Straightness correction is typicallyperformed in a cold state, and thus is also be referred to as “coldworking”. The steps for slender bars having a diameter of φ5 to 7 mm,wires, and plates having a thickness of 8 mm or less may include a heattreatment. Heat treatment is mainly performed after cold working, andheat treatment and cold working are repeated according to the finaldimensions. The smaller the diameter of the final product is and thethinner the final product is, the more cold workability matters,becoming as important as or more important than machinability. The heattreatment may be performed before cold working after hot working.

A low-temperature annealing step is performed after the final step amonga hot working step, a cold working step, a straightness correction step,and an annealing step. When a low-temperature annealing step isperformed, an annealing step is typically performed between the workingsteps. It can be said that a low-temperature annealing step is performedafter the final working step among a hot working step, a cold workingstep, and a straightness correction step.

Specifically, the following are examples of combinations of productionsteps. Hot rolling may be performed instead of hot extrusion.

(1) Hot extrusion and low-temperature annealing

(2) Hot extrusion, cold working (drawing, wire-drawing, rolling), andlow-temperature annealing

(3) Hot extrusion, cold working (drawing, wire-drawing, rolling),straightness correction, and low-temperature annealing

(4) Hot extrusion, repetition of cold working (wire-drawing, rolling)and annealing, cold working, and low-temperature annealing

(5) Hot extrusion, repetition of cold working (cold wire-drawing,rolling) and annealing, cold working, straightness correction, andlow-temperature annealing

(6) Hot extrusion, annealing, cold working (drawing, wire-drawing,rolling), and low-temperature annealing

(7) Hot extrusion, annealing, cold working (drawing, wire-drawing,rolling), straightness correction, and low-temperature annealing

(8) Hot extrusion, annealing, repetition of cold working (drawing,wire-drawing, rolling) and annealing, cold working, and low-temperatureannealing

(9) Hot extrusion, annealing, repetition of cold working (drawing,wire-drawing, rolling) and annealing, cold working, straightnesscorrection, and low-temperature annealing

(10) Hot extrusion, cold-drawing, straightness correction (straightnesscorrection may not be performed), hot forging, and low-temperatureannealing

(11) Hot extrusion, straightness correction, hot forging, andlow-temperature annealing

(12) Hot extrusion, hot forging, and low-temperature annealing

(13) Casting, hot forging, and low-temperature annealing

(14) Casting, straightness correction, hot forging, and low-temperatureannealing

In the free-cutting alloy according to the first or second embodiment ofthe present invention having the above-described constitution, since thealloy's composition, the composition relational expressions, themetallographic structure, the metallographic structure relationalexpressions, and the metallographic structure and composition relationalexpression are defined as described above, even though the Pb content islow, excellent machinability can be obtained, and excellent hotworkability, high strength, and a good balance between strength andductility can be obtained.

Hereinabove, the embodiments of the present invention have beendescribed. However, the present invention is not limited to theembodiments, and appropriate modifications can be made within a rangenot departing from the technical requirements of the present invention.

EXAMPLES

Hereinafter, the results of the experiments that were performed toverify the effects of the embodiments will be described. The followingExamples are for the purpose of explaining the effects of theembodiments. The constituent elements, the processes, and the conditionsdescribed in the Examples do not limit the technical ranges of theembodiments.

Using a low-frequency melting furnace and a semi-continuous castingmachine used on the actual production line, a trial production of copperalloys was performed.

In addition, using a laboratory facility, a trial production of copperalloys was performed.

Tables 9 to 12 show the alloys' compositions. In addition, Tables 13 to19 show production steps. Regarding composition, “MM” refers tomischmetal which represents the total content of rare earth elements.The respective production steps are as follows.

(Steps Nos. A0 to A6, A10, AH1, and AH2)

As shown in Table 13, using the low-frequency melting furnace and thesemi-continuous casting machine on the actual production line, a billethaving a diameter of 240 mm was produced. For raw materials, thosecorrespond to ones used for commercial production were used. The billetwas cut into a length of 800 mm and was heated. Using a hot extruderhaving an officially announced capacity of 3000 tons, two round barshaving a diameter of 25.6 mm were extruded. The extruded bars werecooled at several different cooling rates in a temperature range from530° C. to 450° C. The temperature was measured using a radiationthermometer mainly in a period from the middle stage to the final stageof the hot extrusion process about three or four seconds after the barscame out of the extruder. For the temperature measurement during hotextrusion, hot forging, and hot rolling described below, IGA 8Pro/MB20,a radiation thermometer manufactured by Luma Sense Technologies Inc.,was used.

It was verified that the average temperature of the extruded materialwas within ±5° C. of a temperature shown in Table 13 (in a range of(temperature shown in the table)−5° C. to (temperature shown in thetable)+5° C.)

In Steps Nos. A0, A1, A2, A4, and AH2, the extrusion temperature was590° C. In Step No. A3, the extrusion temperature was 635° C. In StepNo. AH1, the extrusion temperature was 680° C. The average cooling ratein a temperature range from 530° C. to 450° C. after hot extrusion was45° C./min in Step No. A2 and was 65° C./min in Step No. AH2. In stepsother than Steps Nos. A2 and AH2, the average cooling rate was 25°C./min.

After completion of the hot extrusion, in Step No. A0, straightnesscorrection was performed in a cold state. During the straightnesscorrection, the cold working ratio was 0% in effect. In Step No. A4, thedrawing ratio was 8.4%. In steps other than Steps Nos. A0 and A4, theextruded material having a diameter of 25.6 mm was cold-drawn to adiameter of 25.0 mm (working ratio: 4.7%). Further, in Steps Nos. A5 andA6, the material of Step No. A1 was used. In a laboratory, the materialswere put into a mold to perform a low-temperature annealing at 275° C.for 100 minutes and at 410° C. for 50 minutes, respectively. In Step No.A10, the material was hot-extruded to a diameter of 45 mm at 575° C. andwas cooled at an average cooling rate of 20° C./min in a temperaturerange from 530° C. to 450° C. Step No. A10 was also used for a forgingexperiment.

Here, regarding the material on which low-temperature annealing wasperformed, the annealing conditional expression f8 shown below wascalculated.

f 8 = (T − 200) × (t)^(1/2)

T: temperature (material's temperature) (° C.)

t: heating time (min)

In addition, low-temperature annealing was performed on bars arranged(stacked in four tiers) in a steel mold having a recessed cross-section,a width of about 500 mm, a height of 300 mm, a thickness of 10 mm, and alength of 4000 mm. Next, low-temperature annealing was performed, andthe bend of the bars was measured.

All the measurement results of bending was good standing at 0.1 mm orless for one meter of the sample bars obtained by performing Steps Nos.A5 and A6 and Step No. B6 described below on Alloys Nos. S01 and S02.

(Steps Nos. B1 to B7, BH1, and BH2)

As shown in Table 14, using a facility on the actual production line, inSteps Nos. B1 to B7, BH1, and BH2, test materials were hot-extruded to adiameter of 20.0 mm, and were cold-drawn to a diameter of 19.03 mm insteps other than Steps Nos. B5 and B7. In Step No. B5, the material wascold-drawn to a diameter of 18.5 mm. In Steps Nos. B1, B2, B5, B6, andB7, the extrusion temperature was 610° C. Hot extrusion was performed at580° C. in Steps Nos. B3 and BH2, at 640° C. in Step No. B4, and at 680°C. in Step No. BH1. The average cooling rate in a temperature range from530° C. to 450° C. after hot extrusion was 55° C./min in Step No. BH2and was 0.2° C./min in Step No. B2. In the other steps, cooling wasperformed at an average cooling rate of 38° C./min. In Step No. B6, thematerial of Step No. B1 was used and was put into a mold andlow-temperature annealing was performed at 310° C. for 100 minutes. StepNo. E followed Step No. B7.

(Steps Nos. C1 to C3, C10, CH1, and CH2)

As shown in Table 15, in a laboratory, raw materials mixed at apredetermined component ratio were melted. The molten alloy was castinto a mold having a diameter of 100 mm and a length of 180 mm toprepare a billet (Alloys Nos. S51 to S65 and S70 to S84). A molten alloywas obtained from a melting furnace on the actual production line, andimpurities such as Fe or Sn were further intentionally added to themolten alloy. This molten alloy was poured into a mold having a diameterof 100 mm and a length of 180 mm to cast a billet (Alloys Nos. S11 toS17 and Nos. S21 to S26). The concentration of the impurities such as Feor Sn that were intentionally added was lower than or equal to that ofcommercially available brass including Pb.

This billet was heated and extruded into a round bar having a diameterof 22 mm. In Steps Nos. C1, C3, and CH2, the extrusion temperature was595° C. In Step No. C2, the extrusion temperature was 635° C. In StepNo. CH1, the extrusion temperature was 675° C. The average cooling ratein a temperature range from 530° C. to 450° C. after hot extrusion was72° C./min in Step No. CH2 and was 30° C./min in Steps Nos. C1, C2, C3,and CH1. Next, straightness correction was performed (working ratio: 0%)on the bars whose straightness was poor, but not on those having goodstraightness. In Step No. C3, the bar of Step No. C1 was used, andlow-temperature annealing was performed at 320° C. for 60 minutes.

In Step No. C10, a forging material was prepared by extruding a bar to adiameter of 45 mm at an extrusion temperature of 575° C. and cooling thebar at an average cooling rate of 20° C./min.

The above-described alloys A to F were prepared using the method of StepC. The extrusion temperature for the alloys A and D was 750° C., theextrusion temperature for the other alloys, Alloys B, C, E, and F, was635° C., and the average cooling rate in a temperature range from 530°C. to 450° C. after the extrusion was 30° C./min. Alloys A to F were allheat-treated at 500° C. for 2 hours after the extrusion to adjust themetallographic structure. As a comparative material, C3771, a brass forforging including 2 mass % Pb was used, and as Alloy H, a commerciallyavailable material was used.

(Step D)

In Step No. D, a molten alloy was obtained from a laboratory and anotherfrom a melting furnace on the actual production line. They were castinto a metal mold having an inner diameter of 45 mm. The molten alloyswere cooled at an average cooling rate of 40° C./min in a temperaturerange from 530° C. to 450° C. in the process of cooling, and materialsfor forging of Step F was obtained.

(Step E)

As shown in Table 17, Step No. E is a step including annealing. Step No.E is a step of preparing mainly slender bars having a diameter of, forinstance, 7 mm or less. However, as the machining test was unable to beperformed on a slender bar, an extruded bar having a large diameter wasused for the testing instead.

In Step No. E1, a material having a diameter of 20 mm obtained in StepNo. B7 was cold-drawn to a diameter of 16.7 mm, was heat-treated at 480°C. for 60 minutes, and was cold-drawn to a diameter of 16 mm.

In Step No. E2, a material having a diameter of 22 mm obtained in StepNo. C1 was cold-drawn to a diameter of 18.4 mm, heat-treated at 450° C.for 90 minutes, and cold-drawn to a diameter of 17.7 mm.

(Steps Nos. F1 to F5, FH1, and FH2) As shown in Table 18, a round barhaving a diameter of 45 mm obtained in Steps Nos. A10, C10, and D1 werecut to a length of 180 mm. The round bar was horizontally placed and wasforged to a thickness of 16 mm using a press machine having a hotforging press capacity of 150 ton. About three to four secondsimmediately after the material was hot-forged to a predeterminedthickness, the temperature was measured using a radiation thermometerand a contact thermometer. It was verified that the hot forgingtemperature (hot working temperature) was within ±5° C. of a temperatureshown in Table 18 (within a range from (temperature shown in thetable)−5° C. to (temperature shown in the table+5° C.).

In Steps Nos. F1, F2, F3, F5, FH1, and FH2, the hot forging temperatureswere 660° C., 640° C., 615° C., 620° C., 685° C., and 615° C.,respectively. The average cooling rate in a temperature range from 530to 450° C. was set to 63° C./min in Step No. FH2. In the other steps,cooling was performed at an average cooling rate of 28° C./min. In StepF, a forged product which was left as hot-forged without performingstraightness correction (cold working) was obtained. In Step No. F4,low-temperature annealing was performed on the forged product obtainedin Step No. F3 at 290° C. for 100 minutes.

The hot forged material was cut and provided for machining tests andexperiments for investigating mechanical characteristics.

(Step R)

In Step No. R1, a part of the molten alloy from a melting furnace on theactual production line was poured into a casting mold having across-section of 35 mm×70 mm. The surface of the casting was machined todimensions of 32 mm×65 mm×200 mm, and the casting was heated to 650° C.,then two passes of hot-rolling was performed on the casting to athickness of 15 mm. About three or four seconds after completion of thefinal hot rolling, the material's temperature was 560, and the materialwas cooled at an average cooling rate of 20° C./min in a temperaturerange from 530° C. to 450° C. The obtained rolled sheet was cold-rolledto a thickness of 10 mm, was heat-treated at 480° C. or 60 minutes usingan electric furnace, and cold rolling was further performed to athickness of 9 mm.

The above-described test materials were evaluated for the followingitems. The evaluation results are shown in Tables 20 to 32.

(Observation of Metallographic Structure)

The metallographic structure was observed using the following method,then the area ratios (%) of the respective phases such as α phase, βphase, γ phase, κ phase, and μ phase were measured by image analysis. Itwas assumed that α′ phase, β′ phase, and γ′ phase were included in αphase, β phase, and γ phase respectively.

Each of the test materials (bars and forged products) was cut parallelto its long side or parallel to a flowing direction of themetallographic structure. Next, the surface was polished(mirror-polished) and was etched with a mixed solution of hydrogenperoxide and ammonia water. For etching, an aqueous solution obtained bymixing 3 ml of 3 vol % hydrogen peroxide water and 22 ml of 14 vol %ammonia water was used. At a room temperature of about 15° C. to about25° C., the polished metal surface was dipped in the aqueous solutionfor about 2 seconds to about 5 seconds.

The metallographic structure was observed with a metallographicmicroscope at a magnification of 500-fold to obtain the proportions ofthe respective phases and check whether or not any P-containingcompounds were present. Depending on the state of the metallographicstructure, the phases and the compounds were checked at a magnificationof 1000×. In micrographs of five visual fields, respective phases (αphase, β phase, γ phase, κ phase, and μ phase) were manually paintedusing image processing software “Photoshop CC”. Next, the micrographswere binarized using image analysis software “WinROOF 2013” to obtainthe area ratios of the respective phases. Specifically, the average arearatio of each of the phases in the five visual fields was calculated toobtain the proportion of each phase. In this area ratio calculation, theaggregate of the area ratio of each and every constituent phaseexcluding precipitates (P-containing compounds are excluded), oxides,sulfides, and crystallized particles constitutes 100%.

Then P-containing compounds were observed. The minimum size of aprecipitated particle of a P-containing compound that can be observed at500-fold with a metallographic microscope is about 0.5 μm. We firstdetermined whether or not any P-containing compounds were present by theprecipitates that were able be observed with a 500-fold metallographicmicroscope, in the same manner as when the proportion of the phases wereobserved. When P-containing compounds were confirmed under thisobservation condition, the presence of P-containing compounds wasevaluated as “◯” (good). Although depending on the P content and theproduction conditions, there was a sample in which several to severalhundreds P-containing compounds were present in one visual field of themicroscope. As most of the P-containing compounds were present in βphase or at a phase boundary between a phase and β phase, they wereassumed to be included in β phase. In addition, when P-containingcompounds were present in a phase although it was rare, suchP-containing compounds were assumed to be included in α phase. Further,γ phase having a size of less than 0.5 μm was sometimes present in βphase. Phases having a size of less than 0.5 μm are unable to beidentified with a metallographic microscope at a magnification of500-fold. Therefore, in the embodiment, ultrafine γ phase was treated asβ phase. When observed with a metallographic microscope, a P-containingcompound appears blackish grey. Therefore, it is distinguishable from aprecipitate or a compound formed of Mn or Fe which appears light blue.

It is necessary to determine whether an a phase grain is acicular.Accordingly, the shape of a phase was evaluated as follows.

If an α phase crystal grain has the longer side/shorter side ratioexceeding 4, the α phase crystal grain was defined to be acicular(elliptical). If the longer side/shorter side ratio was 4 or lower, theα phase crystal grain was defined to be granular. During the observationof the metallographic structure, the proportion of the number ofgranular α phase crystal grains to the entirety of α phase wasinvestigated. When the proportion of granular α phase crystal grains waslower than 50%, it was evaluated as “X” (poor). When the proportion ofgranular a phase crystal grains was 50% or higher and lower than 75%, itwas evaluated as “Δ” (fair). When the proportion of granular α phasecrystal grains was 75% or higher, it was evaluated as “◯” (good). Theshape of a phase crystal grains affects mechanical characteristics andmachinability, and the more the number of granular a phase crystalgrains, the better the mechanical characteristics and machinability.

Specifically, the area ratio of each of the phases and whether thecompounds were present were evaluated using an image that was printedout in a size of about 70 mm×about 90 mm.

When it was difficult to identify phases and precipitates, they wereidentified by an electron backscattering diffraction pattern(FE-SEM-EBSP) method in which an EDS equipped in an field emissionscanning electron microscope (FE-SEM) (JSM-7000F, manufactured by JEOLLtd.) was used, and phases and precipitates were observed at amagnification of 500-fold or 2000-fold under the conditions of anacceleration voltage of 15 kV and a current value of 15 (set value).

In addition, regarding some alloys, when the Si concentration in β phasewas measured and when it was difficult to determine the presence ofP-containing compound, mainly, quantitative analysis or qualitativeanalysis was performed with an X-ray microanalyzer on a secondaryelectron image and a compositional image taken at a magnification of2000-fold. The measurement was performed using “JXA-8230” (manufacturedby JEOL Ltd.) under the conditions of an acceleration voltage of 20 kVand a current value of 3.0×10⁻⁸ A. In the investigation using theelectron microscope, when P-containing compounds were observed, thealloy was evaluated as “Δ” (fair) in terms of presence of P-containingcompound. When no P-containing compound was observed, the alloy wasevaluated as “X” (poor) in terms of presence of P-containing compound.Those evaluated as “Δ” (fair) regarding presence of P-containingcompound are also acceptable in the embodiment. In the table, theevaluation results regarding the presence of P-containing compounds areshown in the “P Compound” row.

(Electrical Conductivity)

For the measurement of electrical conductivity, a electricalconductivity measurement device (SIGMATEST D2.068, manufactured byFoerster Japan Ltd.) was used. In this specification, the terms“electric conductivity” and “electrical conductivity” are meant to havethe same meaning. In addition, thermal conductivity and electricalconductivity have a strong relation. Therefore, the higher theelectrical conductivity, the better the thermal conductivity.

(Tensile Strength/Elongation)

Each of the test materials was processed in accordance with specimen No.10 of JIS Z 2241, and their tensile strength and elongation weremeasured.

If a hot extruded material or a hot forged material not having undergoneany cold working step has a tensile strength of preferably 470 N/mm² orhigher, more preferably 500 N/mm² or higher, and still more preferably530 N/mm² or higher, the material is considered to have the highestlevel of tensile strength among free-cutting copper alloys. As a result,a reduction in the thickness and weight of parts and components used invarious fields or an increase in allowable stress can be realized. Inaddition, regarding the balance between strength and elongation, whenthe tensile strength is represented by S (N/mm²) and the elongation isrepresented by E (%), if the value of the characteristic relationalexpression f7=S×(100+E)/100 indicating the balance between strength andductility is preferably 600 or higher, more preferably 640 or higher,still more preferably 670 or higher, and still more preferably 700 orhigher, it can be said that the alloy has a very high standard ofbalance between strength and elongation among free-cutting copperalloys.

<Machinability Test Using Lathe>

Machinability was evaluated by the machining test using a lathe asdescribed below.

A hot extruded bar or a hot forged product was machined to prepare atest material having a diameter of 14 mm. A carbide tool (chip) K10 notequipped with a chip breaker was attached to a lathe. Using this lathe,the circumference of the test material having a diameter of 14 mm wasmachined on a dry condition and under the conditions of rake angle: 0°,nose radius: 0.4 mm, clearance angle: 6°, cutting speed: 40 m/min,cutting depth: 1.0 mm, and feed rate: 0.11 mm/rev.

A signal emitted from a dynamometer (AST tool dynamometer AST-TL1003,manufactured by Mihodenki Co., Ltd.) composed of three portions attachedto the tool was electrically converted into a voltage signal andrecorded on a recorder. Next, these signals were converted into cuttingresistance (principal cutting force, feed force, thrust force, N). Inthe machining test, in order to suppress the influence of wear on theinsert, each sample was measured four times by reciprocating A→B→C→ . .. C→B→A twice. The cutting resistance can be obtained from the followingexpression.

Cutting Resistance (Combined Force comprising Principal cutting force,Feed Force, and Thrust Force)=((Principal Cutting Force)²+(FeedForce)²+(Thrust Force)²)^(1/2)

Each sample was measured four times, and the average value thereof wasadopted. Assuming that the cutting resistance of a commerciallyavailable free-cutting brass bar, C3604, made of an alloy including 59mass % Cu, 3 mass % Pb, 0.2 mass % Fe, 0.3 mass % Sn, and Zn as thebalance was 100, a relative value of the cutting resistance(machinability index) of each sample was calculated for relativeevaluation. The higher the machinability index, the better themachinability. Incidentally, “three force components” refers to thecombined force comprising principal cutting force, feed force, andthrust force, which represents the machinability index.

The machinability index was calculated as follows.

Index representing the results of the machining test performed on asample (machinability index)=(cutting resistance of C3604/cuttingresistance of the sample)×100

Concurrently, chips were collected, and the machinability was evaluatedbased on the chip shape. Problems that occur in actual machining areentanglement of chips around the tool and bulking of chips. Therefore,regarding the chip shape, when the average length of the generated chipswas less than 5 mm, it was evaluated as “◯” (good). When the averagelength of the generated chips was 5 mm or more and less than 15 mm, itwas evaluated as “Δ” (fair) determining that machining could beperformed although there could be some practical problems. When theaverage length of the generated chips was 15 mm or longer, it wasevaluated as “X” (poor). Chips generated at the beginning of machiningwere excluded from the subject of the evaluation.

The cutting resistance depends on the shear strength and the tensilestrength of the material, and there is a tendency that the higher thestrength of the material, the higher the cutting resistance. In the caseof a high strength material, if the cutting resistance is approximately40% higher than that of a free-cutting brass bar including 1% to 4 mass% Pb, the cutting resistance is considered to be practically good. Inthe embodiment, the shear strength of the extruded material is about 1.2to 1.3 times that of C3604, a free-cutting brass including 3 mass % Pb.Therefore, in the evaluation of the machinability of the embodiment, amachinability index of about 70 was applied as the standardmachinability index (boundary value). Specifically, when themachinability index was 80 or higher, the machinability was evaluated tobe excellent (evaluation symbol: “@”). When the machinability index was70 or higher and lower than 80, the machinability was evaluated to begood (evaluation symbol: “◯”). When the machinability index was 63 orhigher and lower than 70, the machinability was evaluated to be fair(evaluation symbol: “Δ”). When the machinability index was lower than63, the machinability was evaluated to be poor (evaluation symbol: “X”).

If the alloy's strength is equivalent, there is a correlation betweenchip shape and machinability index. When the machinability index ishigh, chip breakability tends to be good, and this correlation can benumerically expressed.

When cold workability is important, it is necessary that the evaluationresults regarding chip and cutting resistance are at least “fair”.

Incidentally, the machinability index of an alloy comprising 58.1 mass %Cu, 0.01 mass % Pb, and Zn as the balance, which is a free-cuttingcopper alloy having a high Zn concentration and including 0.01 mass % Pband about 50% 3 phase, was 39, and the chip length was longer than 15mm. Likewise, the machinability index of an alloy comprising 55 mass %Cu, 0.01 mass % Pb, and Zn as the balance, which is a β single-phasecopper alloy not including Si and including 0.01 mass % Pb, was 41, andthe chip length was longer than 15 mm.

In Test No. T01 (Alloy No. S01), 0.072 mass % P was included, hotextrusion was performed at 590° C., and P-containing compounds werepresent. The external appearance of the chips generated in Test No. T01(Alloy No. S01) is shown in FIG. 2A. In addition, in Test No. T303(Alloy No. S71), the P content was 0.003 mass % or lower, hot extrusionwas performed at 595° C., and the presence of P-containing compounds wasunable to be confirmed with a metallographic microscope or an electronmicroscope. The external appearance of the chips generated in Test No.T303 (Alloy No. S71) is shown in FIG. 2B.

The average length of the chips generated in Test No. T01 (Alloy No.S01) including P and in which P-containing compounds were observed, was1.2 mm, and the chips were finely broken. On the other hand, in Test No.T303 (Alloy No. S71) in which the P content was 0.003 mass % or lowerand no P-containing compound was observed, the chip length was more than15 mm, and the chips were continuous.

<Drilling Test>

By using a drilling machine with a JIS standard drill made of high speedsteel having a diameter of 3.5 mm attached, 10 mm-deep holes weredrilled on a dry condition at a rotation speed of 1250 rpm and a feedrate of 0.17 mm/rev. Voltage fluctuation in a circumferential directionand an axial direction were measured during drilling using an AST tooldynamometer, and the torque and the thrust during drilling werecalculated. Each sample was measured four times, and the average valuethereof was adopted. Assuming that the torque and the thrust of C3604, acommercially available free-cutting brass bar comprising 59 mass % Cu, 3mass % Pb, 0.2 mass % Fe, 0.3 mass % Sn, and Zn as the balance, was 100,relative values (torque index, thrust index) of the torque and thethrust of the sample were calculated for relative evaluation. The higherthe machinability index (torque index, thrust index, drill index), thebetter the machinability. In the drilling, in order to suppress theinfluence of wear on the drill, each sample was measured four times byreciprocating A→B→C→ . . . C→B→A twice.

That is, the machinability index was obtained as follows.

Index representing Drilling Test Result of Sample (Drill Index)=(TorqueIndex+Thrust Index)/2

Torque Index of Sample=(Torque of C3604/Torque of Sample)×100

Thrust Index of Sample=(Thrust of C3604/Thrust of Sample)×100

During the third test, chips were collected. Machinability was evaluatedbased on the chip shape. Problems that occur in actual machining areentanglement of chips around a tool and bulking of chips. Therefore,regarding chip shape, if the average number of windings per chip wasless than one, it was evaluated as “◯” (good). if the average number ofwindings per chip was one or more and less than three, it was evaluatedas “Δ” (fair) determining that drilling could be performed althoughthere could be some practical problems. If the average number ofwindings per chip was three or more, it was evaluated as “X” (poor).Chips generated at the beginning of drilling were excluded from thesubject of the evaluation.

If the torque and the thrust of a high-strength material are higher thanthe cutting resistance of a free-cutting brass bar including 1% to 4mass % of Pb by about 40% points, the material is considered to bepractically good regarding torque and thrust. In the embodiment, themachinability was evaluated by machinability index with themachinability index of about 70% regarded as the boundary (boundaryvalue). Specifically, when the drill index was 75 or higher, themachinability was evaluated to be excellent (evaluation symbol: “@”).When the drill index was 70 or higher and lower than 75, themachinability was evaluated to be good (evaluation symbol: “◯”). Whenthe drill index was 65 or higher and lower than 70, the machinabilitywas evaluated to be fair (evaluation symbol: “Δ”) determining thatdrilling could be performed although there could be some practicalproblems. When the drill index was lower than 65, the machinability wasevaluated to be poor (evaluation symbol: “X”).

The chip shape and the torque index have a strong relationship if thealloy's strength is the same. When the torque index is high, chipbreakability tends to be high. Therefore, chip shape can be numericallycompared by torque index. In the alloy according to the embodiment, theshear strength, which is more or less proportional to the tensilestrength, is about 1.2 to 1.3 times that of a free-cutting brassincluding 3 mass % Pb. Since cutting resistance has a strongrelationship with shear strength, it is necessary to take the material'sstrength into consideration.

When cold workability, which improves when machinability deteriorates,and vice versa, is important, it is necessary that the evaluationresults regarding chip and cutting resistance are at least “fair” (Δ).

Incidentally, the drill index of an alloy comprising 58.1 mass % Cu,0.01 mass % Pb, and Zn as the balance, which is a free-cutting copperalloy having a high Zn concentration and including 0.01 mass % Pb andabout 50% β phase, was 49 (the torque index was 46, and the thrust indexwas 52), and the number of windings per chip exceeded 3. Likewise, thedrill index of a β single-phase copper alloy comprising 54 mass % Cu,0.01 mass % Pb, and Zn as the balance, which is an alloy not includingSi and including 0.01 mass % Pb, was 61 (the torque index was 53, andthe thrust index was 68), and the number of windings per chip exceeded3.

Regarding tools dedicated to precision drilling, with the recentaccelerated trend toward reduction in the size of various devices andcomponents, drilling of tiny holes on such components is increasinglyrequired. For example, there are a wide range of needs for tools such asthose for drilling pin holes in a metal mold or spinning holes, acomponent of a device relating to a semiconductor such as a printedcircuit board or an optical device. A reduction in the size of variousindustrial products such as home information appliances, medicaldevices, and automobile components is expected to be increasinglyaccelerated. In this trend, drill manufacturers are attempting toimprove the lineup of carbide drills having a diameter of 0.1 mm orless. In the past, the ratio between the diameter and the depth of ahole to be drilled was limited to about 10. However, recently, a numberof drills that are capable of drilling a hole whose ratio between itsdiameter and depth is approximately 100 even if the diameter of the holeis 0.5 mm or less have emerged. e a material having excellentmachinability is required in this field.

(Hot Working Test)

The bar made in Step No. A0 having a diameter of 25.6 mm or the bar madein Step No. C1 having a diameter of 22.0 mm was machined to a diameterof 15 mm and a length of 25 mm. The test material was held at 600° C.for 20 minutes. Subsequently, the test material was vertically placedand compressed to a thickness of 5 mm using an Amsler testing machinehaving a hot compression capacity of 10 tons equipped with an electricfurnace at a strain rate of 0.02/sec and a working ratio of 80%. Duringthe hot working, the test material was held at 600° C.

Hot deformability was evaluated based on whether or not any visiblecracks were present and whether or not a large corrugation was formed onthe surface. e Although depending on the capability of the facility usedor the hot working ratio such as an extrusion ratio, 30 N/mm² is aboundary value of hot deformation resistance up to which commonlymanufactured hot extruded bars can be produced without any problem. In ahot working test performed at 600° C., when cracking did not occur, alarge corrugation was not formed, and hot deformation resistance was 30N/mm² or lower, hot workability was evaluated as good (evaluationsymbol: “◯”). When either hot deformability or hot deformationresistance did not satisfy the above-described standards, hotworkability was evaluated as fair (evaluation symbol: “Δ”) with somereservations. When neither hot deformability nor hot deformationresistance satisfied the above-described standards, hot workability wasevaluated as poor (evaluation symbol: “X”). The evaluation results areshown in Table 32.

Hot extrusion or hot forging at 600° C. is rarely performed on a commoncopper alloy. When a free-cutting copper alloy including Pb is tested at600° C., cracking occurs, and hot deformation resistance exceeds 30N/mm². By performing hot working at a low temperature, high strength,superb balance between high strength and elongation, and excellentmachinability can be obtained, and improvement of dimensional accuracyand an increase in tool life can be realized, which is, in turn,eco-friendly.

In Alloy H, a leaded brass for forging, cracking occurred, anddeformation resistance was high. When the value of the compositionrelational expression f1 was lower than 56.5, a large corrugation wasformed. When the value of the composition relational expression f1 washigher than 59.5, deformation resistance exceeded 30 N/mm².

TABLE 9 Composition Alloy Component Composition (mass %) Impurities(mass %) Relational No. Cu Si P Pb Zn Fe Mn Co Cr Sn Al Bi Ni Sb AgExpression f1 S01 62.9 1.14 0.072 0.009 Balance 0.04 0.02 0.01 0.01 0.030.00 0.01 0.03 0.02 0.01 57.7 S11 62.9 1.15 0.073 0.009 Balance 0.040.02 0.01 0.01 0.03 0.00 0.01 0.03 0.02 0.01 57.7 S12 62.9 1.14 0.0710.009 Balance 0.19 0.07 0.01 0.01 0.03 0.00 0.01 0.03 0.02 0.01 57.7 S1362.8 1.13 0.072 0.009 Balance 0.27 0.18 0.01 0.01 0.03 0.00 0.01 0.030.02 0.01 57.6 S14 62.9 1.13 0.071 0.009 Balance 0.04 0.02 0.01 0.010.18 0.09 0.01 0.03 0.02 0.01 57.7 S15 63.0 1.15 0.070 0.009 Balance0.04 0.02 0.01 0.01 0.29 0.17 0.01 0.03 0.02 0.01 57.8 S16 62.9 1.140.069 0.009 Balance 0.04 0.02 0.01 0.01 0.03 0.00 0.01 0.03 0.02 0.0157.7 S17 62.9 1.15 0.070 0.009 Balance 0.04 0.02 0.01 0.01 0.03 0.000.01 0.03 0.02 0.01 57.7

TABLE 10 Composition Alloy Component Composition (mass %) Impurities(mass %) Relational No . Cu Si P Pb Zn Fe Mn Co Cr Sn Al Bi Ni Se Ag MMExpression f1 S02 64.1 1.21 0.035 0.048 Balance 0.03 0.04 0.00 0.00 0.040.01 0.00 0.07 0.01 0.04 0.02 58.6 S21 63.8 1.20 0.035 0.049 Balance0.09 0.18 0.00 0.00 0.04 0.01 0.00 0.07 0.01 0.04 0.02 58.4 S22 63.91.21 0.034 0.047 Balance 0.18 0.28 0.00 0.00 0.04 0.01 0.00 0.07 0.010.04 0.02 58.4 S23 64.0 1.21 0.036 0.047 Balance 0.03 0.04 0.00 0.000.11 0.18 0.00 0.07 0.01 0.04 0.02 58.5 S24 63.9 1.20 0.034 0.046Balance 0.03 0.04 0.00 0.00 0.29 0.20 0.00 0.07 0.01 0.04 0.02 58.5 S2563.9 1.21 0.033 0.048 Balance 0.03 0.04 0.00 0.00 0.04 0.01 0.00 0.070.01 0.04 0.02 58.4 S26 63.8 1.20 0.034 0.047 Balance 0.03 0.04 0.000.00 0.04 0.01 0.00 0.07 0.01 0.04 0.02 58.4 Note: “MM” refers tomischmetal.

TABLE 11 Composition Relational Alloy Component Composition (mass %)Impurities (mass %) Expression No. Cu Si P Pb Zn Fe Mn Co Cr Sn Al Bi NiSb Ag f1 S51 63.2 1.22 0.021 0.025 Balance 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 57.7 S52 61.8 1.03 0.078 0.008 Balance 0.01 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 57.1 S53 64.6 1.42 0.054 0.011Balance 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 58.1 S54 63.61.26 0.068 0.028 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 57.9 S55 63.8 1.10 0.019 0.055 Balance 0.01 0.00 0.00 0.00 0.110.00 0.00 0.06 0.00 0.00 58.9 S56 62.3 1.06 0.042 0.089 Balance 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 57.5 S57 64.0 1.31 0.0480.025 Balance 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 58.1 S5861.7 1.14 0.043 0.014 Balance 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 56.6 S59 64.9 1.26 0.053 0.026 Balance 0.01 0.00 0.00 0.000.01 0.00 0.00 0.00 0.00 0.00 59.2 S60 63.9 1.08 0.042 0.166 Balance0.01 0.00 0.00 0.02 0.01 0.03 0.00 0.00 0.00 0.00 59.1 S61 64.2 1.190.066 0.074 Balance 0.01 0.00 0.06 0.00 0.00 0.05 0.00 0.00 0.02 0.0058.8 S62 62.6 1.06 0.054 0.056 Balance 0.12 0.04 0.00 0.03 0.00 0.000.01 0.00 0.00 0.00 57.8 S63 63.4 1.12 0.011 0.052 Balance 0.01 0.050.00 0.00 0.00 0.00 0.00 0.06 0.00 0.00 58.4 S64 62.4 1.08 0.047 0.121Balance 0.01 0.00 0.00 0.00 0.07 0.00 0.00 0.12 0.00 0.02 57.5 S65 62.31.05 0.055 0.005 Balance 0.00 0.00 0.03 0.00 0.03 0.11 0.01 0.00 0.020.05 57.5 S66 62.5 1.03 0.078 0.092 Balance 0.01 0.10 0.00 0.00 0.130.00 0.00 0.00 0.00 0.00 57.8

TABLE 12 Composition Relational Alloy Component Composition (mass %)Impurities (mass %) Expression No. Cu Si P Pb Zn Fe Mn Co Cr Sn Al Bi NiSb Ag f1 F 59.6 1.30 0.050 0.010 Balance 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 53.7 S70 61.3 1.17 0.071 0.041 Balance 0.01 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 56.0 S71 62.5 1.05 0.001 0.016Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 57.8 S72 63.51.18 0.001 0.019 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 58.2 S73 65.3 1.56 0.070 0.036 Balance 0.01 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 58.2 S74 65.5 1.48 0.070 0.034 Balance 0.010.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 58.8 S75 66.4 1.65 0.0680.015 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 59.0 S7663.2 0.83 0.057 0.023 Balance 0.02 0.00 0.00 0.00 0.00 0.05 0.00 0.000.00 0.00 59.4 S77 63.7 1.05 0.033 0.001 Balance 0.01 0.00 0.00 0.000.06 0.00 0.00 0.00 0.00 0.00 58.9 S78 63.3 1.09 0.041 0.024 Balance0.26 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 58.4 S79 63.8 1.290.062 0.031 Balance 0.00 0.00 0.00 0.00 0.29 0.17 0.00 0.00 0.00 0.0057.9 S80 64.9 1.10 0.083 0.055 Balance 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 59.9 S81 64.9 1.21 0.065 0.009 Balance 0.01 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 59.4 S82 58.8 0.10 0.010 0.198Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 58.4 S83 63.91.04 0.012 0.015 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 59.2 S84 59.2 0.34 0.055 0.078 Balance 0.05 0.00 0.00 0.00 0.010.00 0.00 0.00 0.00 0.00 57.7 H 58.8 0.00 0.001 2.100 Balance 0.23 0.010.02 0.00 0.29 0.00 0.01 0.03 0.01 0.00 59.8

TABLE 13 Step A: Production step with the facility used formanufacturing products for sale (direct extrusion) Cold Drawing and HotExtrusion Straightness Diameter of Correction Extruded Cooling WorkingLow-Temperature Annealing Step Material Temperature Rate* RatioTemperature Time No. (mm) (° C.) (° C/min) (%) (° C.) (min) f8 Note A025.6 590 25 0 — — — A1 25.6 590 25 4.7 — — — A2 25.6 590 45 4.7 — — — A325.6 635 25 4.7 — — — AH1 25.6 680 25 4.7 — — — AH2 25.6 590 65 4.7 — —— A4 25.6 590 25 8.4 — — — A5 25.6 590 25 4.7 275 100  750 A6 25.6 59025 4.7 410  50 1485 A10 45.0 575 20 — — — — To Step F (forging material)*Cooling rate from 530° C. to 450° C.

TABLE 14 Step B: Production step with the facility used formanufacturing products for sale (indirect extrusion) Combined Drawingand Hot Extrusion Straightness Diameter of Correction Extruded CoolingWorking Low-Temperature Annealing Step Material Temperature Rate* RatioTemperature Time No. (mm) (° C.) (° C./min) (%) (° C.) (min) f8 Note B120.0 610 38 9.5 — — — B2 20.0 610 0.2 9.5 — — — B3 20.0 580 38 9.5 — — —B4 20.0 640 38 9.5 — — — BH1 20.0 680 38 9.5 — — — BH2 20.0 580 55 9.5 —— — B5 20.0 610 38 14.4 — — — B6 20.0 610 38 9.5 310 100 1100Low-temperature annealing was performed on the material of B1 B7 20.0610 38 — — — — To Step E *Cooling rate from 530° C. to 450° C.

TABLE 15 Step C: Extrusion in the Laboratory Hot Extrusion Diameter ofCold Working Extruded Cooling Working Low-Temperature Annealing StepMaterial Temperature Rate* Ratio Temperature Time No. (mm) (° C.) (°C./min) (%) (° C.) (min) f8 Note C1 22.0 595 30 0 — — — Partially toStep E C2 22.0 635 30 0 — — — C3 22.0 595 30 0 320 60 930Low-temperature annealing was performed on the material of C1 CH1 22.0675 30 0 — — — CH2 22.0 595 72 0 — — — C10 45.0 575 20 — — — — To Step F(forging material) *Cooling rate from 530° C. to 450° C.

TABLE 16 Step D: Casting (Production of castings as a forging material)Step Diameter Cooling Rate* No. (mm) (° C./min) D1 45.0 40 *Cooling ratefrom 530° C. to 450° C.

TABLE 17 Step E: Laboratory Cold Drawing 1 Cold Drawing 2 Diameter ofDiameter Diameter Material Extruded of Drawn Working Annealing of DrawnWorking Step (preceding Material Material Ratio Temperature TimeMaterial Ratio No. step) (mm) (mm) (%) (° C.) (min) (mm) (%) E1 B7 20.016.7 30.3 480 60 16.0 8.2 E2 C1 22.0 18.4 30.0 450 90 17.7 7.5

TABLE 18 Step F: Hot Forging Hot Forging Cold Working Material CoolingWorking Low-Temperature Annealing Step (preceding Temperature Rate*Ratio Temperature Time No. step) (° C.) (° C./min) (%) (° C.) (min) f8Note F1 A10, C10 660 28 0 — — — F2 A10, C10 640 28 0 — — — F3 A10, C10615 28 0 — — — F4 A10, C10 615 28 0 290 100 900 Low-temperatureannealing was performed on the material of F3 FH1 A10, C10 685 28 0 — —— FH2 A10, C10 615 63 0 — — — F5 D1 620 28 0 — — — *Cooling rate from530° C. to 450° C.

TABLE 19 Step R: Rolling in the Laboratory Hot Rolling Cold Rolling 1Cold Rolling 2 Thickness Thickness Thickness of Hot- of Cold- of Cold-Rolled Final Cooling Rolled Working Annealing Rolled Working StepMaterial Temperature Rate* Material Ratio Temperature Time MaterialRatio No. (mm) (° C.) (° C./min) (mm) (%) (° C.) (min) (mm) (%) R1 15.0560 20 10.0 33.3 480 60 9.0 10.0 *Cooling rate from 530° C. to 450° C.

TABLE 20 Metallographic Structure Si Shape Concentration Test Alloy Stepof α in β phase No. No. No. f2 f3 f4 f5 f6 f6A P Compound phase (mass %)T01 S01 A0 52 48 0 0 51 59 ◯ ◯ 1.4 T02 A1 52 48 0 0 51 59 ◯ ◯ 1.4 T03 A250 50 0 0 53 61 ◯ ◯ — T04 A3 49 51 0 0 54 62 ◯ Δ 1.4 T05 AH1 46 54 0 058 65 ◯ X — T06 AH2 49 51 0 0 54 62 Δ ◯ — T07 A4 52 48 0 0 51 59 ◯ ◯ —T08 A5 53 46 0.7 0.3 52 59 ◯ ◯ — T09 A6 54 44 1.6 0.7 51 58 ◯ ◯ 1.4 T10A10 54 46 0 0 49 56 ◯ ◯ — T11 B1 48 52 0 0 56 63 ◯ ◯ — T12 B2 53 47 0 050 58 ◯ ◯ — T13 B3 49 51 0 0 54 62 ◯ ◯ 1.4 T14 B4 44 56 0 0 60 67 ◯ Δ —T15 BH1 42 58 0 0 62 69 ◯ X — T16 BH2 45 55 0 0 59 66 Δ ◯ — T17 B5 49 510 0 54 62 ◯ ◯ — T18 B6 52 46 1.3 0.5 53 60 ◯ ◯ — T21 F1 46 54 0 0 58 65◯ Δ — T22 F2 50 50 0 0 53 61 ◯ ◯ 1.4 T23 F3 51 49 0 0 52 60 ◯ ◯ — T24 F452 47 0.9 0.3 53 60 ◯ ◯ — T25 FH1 43 57 0 0 61 68 ◯ X 1.3 T26 FH2 48 520 0 56 63 Δ ◯ — T27 F5 50 50 0 0 53 61 ◯ ◯ — T101 S11 C1 52 48 0 0 51 59◯ ◯ 1.4 T102 S12 C1 54 46 0 0 49 56 ◯ ◯ 1.3 T103 S13 C1 58 42 0 0 45 52◯ ◯ — T104 S14 C1 53 46 0.9 0.4 52 59 ◯ ◯ 1.4 T105 S15 C1 58 39 3.5 1.647 55 ◯ ◯ — T106 S16 E1 59 41 0 0 44 51 ◯ ◯ 1.5 T107 S17 R1 57 43 0 0 4653 ◯ ◯ 1.4

TABLE 21 Property Electrical Tensile Test Alloy Step ConductivityStrength Elongation No. No. No. (% IACS) (N/mm²) (%) f7 T01 S01 A0 15.7536 33 713 T02 A1 15.7 573 26 722 T03 A2 15.7 585 25 731 T04 A3 15.8 55925 699 T05 AH1 15.9 535 25 669 T06 AH2 15.3 570 27 724 T07 A4 15.6 62722 765 T08 A5 16.0 586 24 727 T09 A6 16.1 563 23 692 T10 A10 15.9 520 37712 T11 B1 15.7 660 19 785 T12 B2 15.4 638 20 766 T13 B3 15.6 684 18 807T14 B4 15.7 642 18 758 T15 BH1 15.9 621 19 739 T16 BH2 15.3 676 18 798T17 B5 15.6 702 14 800 T18 B6 16.0 675 17 790 T21 F1 15.8 505 29 651 T22F2 15.7 530 31 694 T23 F3 15.7 547 30 711 T24 F4 15.9 534 27 678 T25 FH115.8 496 27 630 T26 FH2 15.4 540 32 713 T27 F5 15.6 528 29 681 T101 S11C1 15.8 532 34 713 T102 S12 Cl 15.4 533 31 698 T103 S13 C1 15.2 538 25673 T104 S14 C1 15.5 527 28 675 T105 S15 C1 15.6 490 18 578 T106 S16 E115.6 602 21 728 T107 S17 R1 15.5 — — —

TABLE 22 Lathe Three Force Drill Test Alloy Step Compo- Torque ThrustDrill No. No. No. Chips nents Chips Index Index Index T01 S01 A0 ◯ 87 ◯75 76 76 T02 A1 ◯ 86 ◯ 76 75 76 T03 A2 ◯ 86 ◯ 75 75 75 T04 A3 ◯ 84 ◯ 7376 75 T05 AH1 ◯ 83 ◯ 72 74 73 T06 AH2 Δ 80 Δ 70 75 73 T07 A4 ◯ 85 ◯ 7773 75 T08 A5 ◯ 88 ◯ 79 71 75 T09 A6 ◯ 85 ◯ 78 71 75 T10 A10 ◯ 85 ◯ 73 7675 T11 B1 ◯ 87 ◯ 76 73 75 T12 B2 ◯ 85 ◯ 73 75 74 T13 B3 ◯ 88 ◯ 77 72 75T14 B4 ◯ 85 ◯ 75 74 75 T15 BH1 ◯ 84 ◯ 73 74 74 T16 BH2 ◯ 82 ◯ 73 75 74T17 B5 ◯ 87 ◯ 78 71 75 T18 B6 ◯ 86 ◯ 80 71 76 T21 F1 ◯ 84 ◯ 74 77 76 T22F2 ◯ 86 ◯ 75 77 76 T23 F3 ◯ 88 ◯ 76 75 76 T24 F4 ◯ 87 ◯ 78 74 76 T25 FH1◯ 83 ◯ 73 77 75 T26 FH2 ◯ 82 Δ 71 76 74 T27 F5 ◯ 86 ◯ 74 78 76 T101 S11C1 ◯ 86 ◯ 75 75 75 T102 S12 C1 ◯ 84 ◯ 73 74 74 T103 S13 C1 Δ 75 Δ 67 7169 T104 S14 C1 ◯ 85 ◯ 75 72 74 T105 S15 C1 Δ 77 ◯ 73 64 69 T106 S16 E1 ◯82 ◯ 72 74 73 T107 S17 R1 — — ◯ 71 77 74

TABLE 23 Metallographic Structure Si Shape Concentration Test Alloy Stepof α in β phase No. No. No. f2 f3 f4 f5 f6 f6A P Compound phase (mass %)T31 S02 A0 63 37 0 0 41 51 ◯ ◯ — T32 A1 64 36 0 0 40 50 ◯ ◯ — T33 A2 6238 0 0 42 52 ◯ ◯ — T34 A3 60 40 0 0 44 54 ◯ ◯ — T35 AH1 56 44 0 0 48 59◯ X — T36 AH2 59 41 0 0 45 56 X ◯ — T37 A4 62 38 0 0 42 52 ◯ ◯ — T38 A566 32 1.9 1.1 39 50 ◯ ◯ — T39 A6 67 29 3.4 2.1 37 48 ◯ ◯ 1.5 T40 A10 6436 0 0 40 50 ◯ ◯ — T41 F1 57 43 0 0 47 58 ◯ ◯ — T42 F2 59 41 0 0 45 56 ◯◯ 1.5 T43 F3 61 39 0 0 43 53 ◯ ◯ — T44 F4 63 34 2.4 1.3 42 53 ◯ ◯ — T45FH1 55 45 0 0 50 60 ◯ X — T46 FH2 58 42 0 0 46 57 Δ ◯ — T47 F5 60 40 0 044 54 ◯ ◯ — T111 S21 C1 64 36 0 0 39 50 ◯ ◯ 1.5 T112 S22 C1 69 31 0 0 3444 ◯ ◯ — T113 S23 C1 64 35 0.9 0.5 41 52 ◯ ◯ 1.5 T114 S24 C1 69 26 4.12.8 35 45 ◯ ◯ — T115 S25 E1 69 31 0 0 34 44 ◯ ◯ 1.6 T116 S26 R1 67 33 00 36 46 ◯ ◯ —

TABLE 24 Property Electrical Tensile Test Alloy Step ConductivityStrength Elongation No. No. No. (% IACS) (N/mm²) (%) f7 T31 S02 A0 15.1516 36 702 T32 A1 15.0 557 30 724 T33 A2 15.2 563 29 726 T34 A3 15.2 55128 705 T35 AH1 15.3 535 28 685 T36 AH2 15.0 567 29 731 T37 A4 15.2 60221 728 T38 A5 15.5 571 24 708 T39 A6 15.4 566 21 685 T40 A10 15.1 505 39702 T41 F1 15.3 500 33 665 T42 F2 15.2 522 35 705 T43 F3 15.2 536 34 718T44 F4 15.3 530 25 663 T45 FH1 15.2 482 33 641 T46 FH2 15.1 541 35 730T47 F5 15.4 523 32 690 T111 S21 C1 14.9 512 36 696 T112 S22 C1 14.6 50829 655 T113 S23 C1 15.1 500 35 675 T114 S24 C1 14.9 468 20 562 T115 S25E1 15.1 585 22 714 T116 S26 R1 15.0 — — —

TABLE 25 Lathe Three Force Drill Test Alloy Step Compo- Torque ThrustDrill No. No. No. Chips nents Chips Index Index Index T31 S02 A0 ◯ 83 ◯74 75 75 T32 A1 ◯ 84 ◯ 75 74 75 T33 A2 ◯ 83 ◯ 73 73 73 T34 A3 ◯ 82 ◯ 7174 73 T35 AH1 ◯ 80 Δ 70 73 72 T36 AH2 Δ 77 X 69 73 71 T37 A4 ◯ 82 ◯ 7473 74 T38 A5 ◯ 83 ◯ 75 70 73 T39 A6 ◯ 80 ◯ 74 68 71 T40 A10 ◯ 81 ◯ 73 7474 T41 F1 ◯ 83 ◯ 72 75 74 T42 F2 ◯ 85 ◯ 75 76 76 T43 F3 ◯ 85 ◯ 76 77 77T44 F4 ◯ 84 ◯ 77 71 74 T45 FH1 ◯ 82 ◯ 71 74 73 T46 FH2 Δ 80 Δ 70 76 73T47 F5 ◯ 83 ◯ 72 77 75 T111 S21 C1 ◯ 82 ◯ 71 73 72 T112 S22 C1 X 70 Δ 6570 68 T113 S23 C1 ◯ 83 ◯ 75 70 73 T114 S24 C1 X 71 Δ 72 65 69 T115 S25E1 ◯ 77 ◯ 69 72 71 T116 S26 R1 — — ◯ 70 73 72

TABLE 26 Metallographic Structure Si Shape Concentration Test Alloy Stepof α in β phase No. No. No. f2 f3 f4 f5 f6 f6A P Compound phase (mass %)T201 S51 C1 53 47 0 0 52 60 ◯ ◯ 1.5 T202 C3 54 43 2.8 1.2 53 60 ◯ ◯ 1.5T203 F2 50 50 0 0 55 63 ◯ ◯ — T204 F3 52 48 0 0 53 61 ◯ ◯ — T205 S52 C139 61 0 0 62 69 ◯ ◯ 1.2 T206 S53 C1 72 23 4.8 3.8 34 41 ◯ ◯ — T207 C3 7615 8.2 9.8 26 34 ◯ ◯ — T208 F3 69 28 2.9 1.9 38 46 ◯ ◯ 1.7 T209 S54 C156 44 0 0 49 59 ◯ ◯ — T210 C2 53 47 0 0 53 63 ◯ ◯ — T211 CH1 51 49 0 055 65 ◯ X — T212 F2 52 48 0 0 54 64 ◯ ◯ — T213 F3 55 45 0 0 51 60 ◯ ◯1.5 T214 S55 C1 66 34 0 0 36 46 ◯ ◯ — T215 C2 64 36 0 0 38 48 ◯ ◯ — T216CH2 62 38 0 0 40 50 X ◯ — T217 E2 70 30 0 0 31 42 ◯ ◯ 1.5 T218 F1 62 380 0 40 50 ◯ ◯ — T219 F2 64 36 0 0 38 48 ◯ ◯ 1.4 T220 FH2 61 39 0 0 41 51X ◯ — T221 S56 C1 46 54 0 0 56 69 ◯ ◯ 1.3 T222 F5 44 56 0 0 58 71 ◯ ◯1.3 T223 S57 C1 61 38 0.8 0.4 46 55 ◯ ◯ 1.6 T224 S58 C1 26 74 0 0 79 86◯ Δ 1.3 T225 S59 C1 77 21 1.8 1.5 28 37 ◯ ◯ — T226 C3 83 11 5.6 9.2 1929 ◯ ◯ — T227 S60 C1 70 30 0 0 31 49 ◯ ◯ 1.3 T228 S61 C1 64 36 0 0 39 53◯ ◯ 1.5 T229 S62 C1 50 50 0 0 51 63 ◯ ◯ 1.3 T230 S63 C1 61 39 0 0 41 51Δ ◯ 1.4 T231 F2 61 39 0 0 41 51 Δ ◯ — T232 FH2 58 42 0 0 43 53 X ◯ —T233 S64 C1 46 54 0 0 56 72 ◯ ◯ 1.3 T234 S65 C1 46 54 0 0 55 61 ◯ ◯ 1.3T235 S66 C1 52 48 0 0 49 64 ◯ ◯ 1.3

TABLE 27 Property Electrical Test Alloy Step Conductivity TensileStrength Elongation No. No. No. (% IACS) (N/mm²) (%) f7 T201 S51 C1 15.4542 33 721 T202 C3 15.6 518 26 653 T203 F2 15.5 535 30 696 T204 F3 15.4554 30 720 T205 S52 C1 16.6 563 24 698 T206 S53 C1 13.6 539 23 663 T207C3 13.8 506 17 592 T208 F3 13.6 545 26 687 T209 S54 C1 15.2 539 35 728T210 C2 15.2 526 35 710 T211 CH1 15.3 487 36 662 T212 F2 15.2 530 32 700T213 F3 15.2 549 31 719 T214 S55 C1 15.6 507 39 705 T215 C2 15.7 490 38676 T216 CH2 15.9 500 40 700 T217 E2 15.5 592 24 734 T218 F1 15.9 498 37682 T219 F2 15.6 511 36 695 T220 FH2 16.1 518 36 704 T221 S56 C1 16.5547 28 700 T222 F5 16.6 538 26 678 T223 S57 C1 14.4 545 28 698 T224 S58C1 16.6 583 20 700 T225 S59 C1 14.8 517 27 657 T226 C3 15.2 496 21 600T227 S60 C1 16.0 498 40 697 T228 S61 C1 15.1 498 38 687 T229 S62 C1 16.3533 29 688 T230 S63 C1 15.9 514 38 709 T231 F2 15.9 518 37 710 T232 FH215.8 522 37 715 T233 S64 C1 16.3 545 28 698 T234 S65 C1 16.6 547 29 706T235 S66 C1 16.7 532 31 697

TABLE 28 Lathe Three Force Drill Test Alloy Step Compo- Torque ThrustDrill No. No. No. Chips nents Chips Index Index Index T201 S51 C1 ◯ 84 ◯74 75 75 T202 C3 ◯ 85 ◯ 77 71 74 T203 F2 ◯ 84 ◯ 73 75 74 T204 F3 ◯ 87 ◯76 76 76 T205 S52 C1 ◯ 86 ◯ 76 75 76 T206 S53 C1 ◯ 79 ◯ 74 69 72 T207 C3Δ 72 ◯ 71 65 68 T208 F3 ◯ 83 ◯ 75 72 74 T209 S54 C1 ◯ 87 ◯ 76 75 76 T210C2 ◯ 86 ◯ 73 75 74 T211 CH1 ◯ 83 ◯ 71 74 73 T212 F2 ◯ 87 ◯ 74 76 75 T213F3 ◯ 87 ◯ 76 77 77 T214 S55 C1 ◯ 81 ◯ 73 74 74 T215 C2 ◯ 80 ◯ 71 75 73T216 CH2 X 72 Δ 68 72 70 T217 E2 Δ 76 ◯ 69 74 72 T218 F1 ◯ 81 ◯ 71 76 74T219 F2 ◯ 82 ◯ 73 75 74 T220 FH2 X 73 Δ 69 73 71 T221 S56 C1 ◯ 90 ◯ 7876 77 T222 F5 ◯ 89 ◯ 77 76 77 T223 S57 C1 ◯ 87 ◯ 76 73 75 T224 S58 C1 ◯90 ◯ 76 78 77 T225 S59 C1 Δ 75 ◯ 72 68 70 T226 C3 X 71 Δ 68 64 66 T227S60 C1 ◯ 83 ◯ 74 75 75 T228 S61 C1 ◯ 85 ◯ 74 76 75 T229 S62 C1 ◯ 88 ◯ 7675 76 T230 S63 C1 Δ 76 Δ 70 74 72 T231 F2 Δ 77 ◯ 71 74 73 T232 FH2 X 71X 67 73 70 T233 S64 C1 ◯ 91 ◯ 78 78 78 T234 S65 C1 ◯ 87 ◯ 74 75 75 T235S66 C1 ◯ 89 ◯ 76 78 77

TABLE 29 Metallographic Structure Si Shape Concentration Test Alloy Stepof α in β phase No. No. No. f2 f3 f4 f5 f6 f6A P Compound phase (mass %)T301 F C1 0 100 0 0 — — ◯ — — T302 S70 C1 17 83 0 0 90 101  ◯ X — T303S71 C1 55 45 0 0 46 51 X ◯ — T304 C3 57 43 0.5 0.2 46 51 X ◯ — T305 F252 48 0 0 49 54 X ◯ — T306 F4 56 44 0.5 0.2 47 52 X ◯ — T307 S72 C1 6040 0 0 43 49 X ◯ — T308 C3 63 35 1.8 0.9 42 47 X ◯ — T309 S73 C1 70 1910.8 10.2 34 44 ◯ ◯ — T310 S74 C1 74 17 8.8 9.3 30 40 ◯ ◯ — T311 S75 C178 9 12.7 25.4 22 30 ◯ ◯ — T312 S76 C1 77 23 0 0 21 30 ◯ ◯ — T313 S77 C171 29 0 0 30 34 ◯ ◯ — T314 S78 C1 68 32 0 0 33 42 ◯ ◯ — T315 S79 C1 6827 4.8 3.2 37 47 ◯ ◯ — T316 S80 C1 83 16 0.3 0.3 18 31 ◯ ◯ — T317 S81 C181 17 1.8 1.9 23 30 ◯ ◯ — T318 S82 C1 57 43 0 0 14 31 — — 0.1 T319 S83C1 75 25 0 0 25 31 Δ ◯ — T320 S84 C1 53 47 0 0 27 41 ◯ ◯ 0.4 T321 H C1 —— — — — — — — —

TABLE 30 Property Electrical Test Alloy Step Conductivity TensileStrength Elongation No. No. No. (% IACS) (N/mm²) (%) f7 T301 F C1 16.9 —— — T302 S70 C1 16.9 570 15 656 T303 S71 C1 17.1 522 36 710 T304 C3 16.9527 35 711 T305 F2 17.1 530 36 721 T306 F4 16.9 536 34 718 T307 S72 C115.7 518 33 689 T308 C3 15.7 511 26 644 T309 S73 C1 12.8 519 14 592 T310S74 C1 13.2 508 15 584 T311 S75 C1 12.0 467 12 523 T312 S76 C1 17.9 45238 624 T313 S77 C1 16.1 474 39 659 T314 S78 C1 15.9 500 31 655 T315 S79C1 14.5 490 16 568 T316 S80 C1 15.6 455 39 632 T317 S81 C1 15.9 498 28637 T318 S82 C1 — 416 42 591 T319 S83 C1 15.9 478 38 660 T320 S84 C123.1 450 32 594 T321 H C1 — — — —

TABLE 31 Lathe Three Force Drill Test Alloy Step Compo- Torque ThrustDrill No. No. No. Chips nents Chips Index Index Index T301 F C1 ◯ 93 ◯74 77 76 T302 S70 C1 ◯ 92 ◯ 75 77 76 T303 S71 C1 X 69 X 67 74 71 T304 C3X 68 Δ 69 71 70 T305 F2 X 69 X 68 74 71 T306 F4 X 70 Δ 70 70 70 T307 S72C1 Δ 73 X 67 73 70 T308 C3 X 70 Δ 68 71 70 T309 S73 C1 Δ 73 ◯ 74 66 70T310 S74 C1 Δ 72 ◯ 73 68 71 T311 S75 C1 X 58 X 61 57 59 T312 S76 C1 X 69Δ 66 69 68 T313 S77 C1 X 70 Δ 68 71 70 T314 S78 C1 X 70 X 64 71 68 T315S79 C1 X 73 Δ 74 65 70 T316 S80 C1 X 64 X 66 68 67 T317 S81 C1 X 69 Δ 6966 68 T318 S82 C1 X 52 X 55 61 58 T319 S83 C1 X 68 X 67 71 69 T320 S84C1 X 61 X 63 68 66 T321 H C1 — — — — — —

TABLE 32 Test Alloy Step Hot No. No. No. Workability T01 S01 A0 ◯ T102S12 C1 ◯ T104 S14 C1 ◯ T31 S02 A0 ◯ T111 S21 C1 ◯ T113 S23 C1 ◯ T201 S51C1 ◯ T205 S52 C1 ◯ T206 S53 C1 ◯ T209 S54 C1 ◯ T214 S55 C1 ◯ T221 S56 C1◯ T223 S57 C1 ◯ T224 S58 C1 ◯ T225 S59 C1 ◯ T227 S60 C1 ◯ T228 S61 C1 ◯T229 S62 C1 ◯ T230 S63 C1 ◯ T233 S64 C1 ◯ T234 S65 C1 ◯ T301 F C1 Δ T302S70 C1 Δ T303 S71 C1 ◯ T307 S72 C1 ◯ T309 S73 C1 ◯ T310 S74 C1 ◯ T311S75 C1 ◯ T312 S76 C1 ◯ T313 S77 C1 ◯ T316 S80 C1 Δ T320 S84 C1 ◯ T321 HC1 X

From the above-described measurement results, the following findingswere obtained.

1) By satisfying the composition according to the embodiment, thecomposition relational expression f1, the requirements regarding themetallographic structure, the metallographic structure relationalexpressions f2 to f6, and the metallographic structure and compositionrelational expression f6A, excellent machinability can be obtained evenif the content of Pb is small, and a hot extruded material, a hot forgedmaterial, or a hot rolled material having good hot workability at about600° C., high electrical conductivity of 13% IACS or higher, highstrength, good ductility, and superb balance between strength andductility (characteristic relational expression f7) can be obtained(Alloys Nos. S01, S02, S11, S12, S14, S16, S17, S21, S23, S25, and S51to S66).

2) By including P in excess of 0.003 mass % and causing P-containingcompounds to be present in β phase, chip breakability was improved andcutting resistance was reduced. When the P content was 0.02 mass % orhigher, machinability further improved. Even when the amount of γ phasewas 0%, excellent machinability was able to be maintained (for example,Alloys Nos. S01 and S02).

3) When the Cu content was low, the amount of β phase increased, and theelongation decreased. When the Cu content was high, the amount of βphase decreased, the amount of γ phase increased, the elongation valuelowered, the balance between strength and ductility deteriorated, andmachinability was not good (Alloys Nos. S70, S73, and S74).

4) When the Si content was low, machinability deteriorated. When the Sicontent was high, the amount of γ phase increased, the elongation valuelowered, the balance between strength and ductility deteriorated, theelectrical conductivity was low, and machinability was not good (AlloysNos. S73, S75, S76, and S84).

5) When the Si content in β phase was in a range of 1.2 mass % or higherand 1.7 mass % or lower, excellent machinability was obtained (AlloysNos. S01, S02, S56, and S57).

6) When the P content was 0.003 mass % or lower, chip breakabilitydeteriorated and cutting resistance increased in both lathing anddrilling (Alloys Nos. S71 and S72).

When P content was about 0.01 mass %, P-containing compounds could notbe observed with a metallographic microscope but could be observed withan electron microscope. When the P content was about 0.02 mass % orhigher, P-containing compounds began to be observed with ametallographic microscope at a magnification of 500-fold or 1000-fold,and machinability further improved (Alloys Nos. S63, S51, and S55). WhenP-containing compounds were unable to be observed with an electronmicroscope but were able to be observed with a metallographicmicroscope, the effect of P-containing compounds on machinability wasslightly reduced (for example, Alloys Nos. S63 and S72). When etchingwas performed, even if the etching conditions were the same, if the Pcontent in the metallographic structure was higher than about 0.01 mass% to 0.02 mass %, the boundaries between α phase and β phase becameclear. It is presumed that this phenomenon relates tosolid-solubilization of P in β phase, whether or not any P-containingcompounds are present, and the form of P-containing compounds that arepresent.

7) When the Pb content was lower than 0.003 mass %, machinability waspoor (Alloy No. S77). When the Pb content was 0.005 mass % or higher,machinability improved, and when it was 0.01 mass % or higher,machinability further improved. When the Pb content was higher than 0.05mass %, machinability improved still further (Alloys Nos. S60, S65, andS66). Even when the Pb content was about 0.2 mass % and the amount of βphase was large, if the Si content was low, the effect of Pb onmachinability was small, and the alloy's machinability was poor (AlloyNo. S82).

8) It was verified that, even if inevitable impurities are included inan amount actually included in a commercially manufactured alloy, thereis no significant influence on the properties (Alloys Nos. S01, S02, andS11). It is presumed that when Fe, Mn, Co, or Cr is contained in anamount exceeding the preferable range of inevitable impurities,intermetallic compounds comprising Fe, Mn, or the like and Si or P areformed. As a result, it is presumed that the machinability deteriorateddue to the presence of compounds comprising Fe or the like and Si, and adecrease in the concentration of Si that was acting effectively. Inaddition, it is presumed that the composition of P-containing compoundsmay have changed (Alloys Nos. S12, S13, S21, S22, and S78). When Sn andAl were contained in an amount exceeding the preferable range ofinevitable impurities, the elongation value decreased due to an increasein the amount of γ phase, and machinability deteriorated. It is presumedthat γ phase or β phase includes a large amount of Sn or Al, and thecharacteristics of γ phase or β phase having a small amount ofinevitable impurities may have changed (Alloys Nos. S14, S15, S23, S24,and S79).

9) When the composition relational expression f1 was low, the elongationvalue decreased. When the composition relational expression f1 was high,machinability deteriorated. When the composition relational expressionf1 was higher than 59.5 or lower than 56.5, hot workability,machinability, and/or mechanical characteristics did not reach therespective target values (Alloys Nos. S70 and S80). When the value ofthe composition relational expression f1 was 57.0 or higher, theelongation value further improved. When the value of the compositionrelational expression f1 was 57.5 or higher, the elongation valuefurther improved. On the other hand, when the value of the compositionrelational expression f1 was 59.0 or lower, machinability furtherimproved. When the value of the composition relational expression f1 was58.5 or lower, machinability improved still further (for example, AlloysNos. S01 and S02).

10) When the area ratio of 3 phase was lower than 15%, even though thecomposition and composition relational expression f1 were satisfied,excellent machinability was not obtained. When the area ratio of β phasewas higher than 80%, the elongation value was low (Alloys Nos. S70, S75,and S59).

When the proportion of β phase was 70% or higher, the cutting resistancewas substantially the same as that of a β single-phase alloy including1.3 mass % Si and 0.05 mass % P in which P-containing compounds werepresent (Alloys F, S58, and S70). When the proportion of β phase wasabout 40% or 50% or higher or when the metallographic structurerelational expression f6 was about 45 or higher, and the metallographicstructure and composition relational expression f6A was about 55 orhigher, the machinability of the β single-phase alloy or Alloy F wasmaintained (for example, Alloys Nos. S54, S56, S64, and S65).

11) Even when the area ratio of γ phase was 0%, by causing anappropriate amount of β phase to be present, excellent machinability andmechanical characteristics were obtained (for example, Alloys Nos. S01and S02).

12) When the area ratio of γ phase was 8% or higher, the elongationvalue decreased. When the amount of γ phase was appropriate, the torqueindex improved. When the metallographic structure relational expressionf5=18×(γ)/(β)≥9, the elongation value and machinability were low. Whenthe metallographic structure relational expression f5=18×(γ)/(β)<2, adecrease in ductility was small, and the torque and the turningperformance improved (Alloys Nos. S73 and S74, Alloy No. S01, and StepsNos. A5 and A6).

13) Even when the requirements regarding the composition and themetallographic structure, represented by f2 to f4, and f6, weresatisfied, if the metallographic structure and composition relationalexpression f6A was low, machinability was poor (Alloys Nos. S81 andS83). When f6A was 44 or higher, machinability further improved. Whenf6A was about 55 or higher, machinability improved even further (forexample, Alloys Nos. S51, S57, S62, and S66).

14) When the proportion of granular (longer side/shorter side≤4) α phasecrystal grains was 75% or higher, strength and machinability furtherimproved. It is presumed that, when the average size of α phase crystalgrains was 30 μm or less and α phase crystal grains were fine andgranular, a phase functioned as a cushioning material, phase boundariesbetween α phase and β phase functioned as stress concentration sourcesduring machining, and chip breakability improved. Even when theproportion of granular a phase crystal grains was lower than 50%,targeted machinability and mechanical characteristics were obtained (forexample, Alloys Nos. S01, S51 to S66, and Step Nos. A1 to A3, and AH1).

15) When the composition according to the embodiment and the compositionrelational expression f1 were satisfied, hot workability at 600° C. wasexcellent, and hot extrusion, hot forging, and hot rolling were able tobe performed at about 600° C. When the hot working temperature was 675°C. or higher, the proportion of granular a phase was lower than 50% (forexample, Alloys Nos. S01 and S02). In addition, even when a casting wasused as a forging material, hot forgeability at 620° C. was excellent,and machinability and mechanical characteristics were also excellent(Step No. F5).

16) When the hot extrusion temperature was higher than about 650° C.,tensile strength decreased, and machinability slightly deteriorated.When extrusion was performed at about 625° C. or lower, mechanicalcharacteristics and machinability improved.

When the forging temperature during hot forging was higher than about675° C., tensile strength decreased, and machinability slightlydeteriorated. When forging was performed at about 650° C. or lower orabout 625° C. or lower, mechanical characteristics and machinabilityimproved.

17) When the composition and the relational expressions f1 to f6A weresatisfied, the tensile strength of a hot extruded material or a forgedproduct not having undergone cold working was high e at 470 N/mm² orhigher. When the composition and the values of the relationalexpressions were within the preferable ranges, the tensile strengthexceeded 500 N/mm². In addition, the characteristic relationalexpression f7=S×(100+E)/100 indicating the balance between strength andductility was 600 or higher. When the composition and the values of therelational expressions were in the preferable ranges, the characteristicrelational expression f7 was high standing at 640 or higher or 670 orhigher. When the shape of a phase and the production conditions deviatedfrom the preferable ranges, the tensile strength and the characteristicrelational expression f7 decreased, but the tensile strength was 470N/mm² or higher and f7 was 600 or higher (Alloys Nos. S01, S02, and S51to S66 and the respective steps).

18) If the composition and the relational expressions f1 to f6A weresatisfied, when the cold working ratio during cold working wasrepresented by [R]%, the tensile strength was all (470+8×[R]) N/mm² orhigher, more specifically, (500+8×[R]) N/mm² or higher, and theelongation E (%) was all (0.02×[R]²−1.15×[R]+18)% or higher, morespecifically, all (0.02×[R]²−1.2×[R]+20)% or higher (Steps Nos. A1 toA6, B1 to B6, E1, and E2).

19) Although depending on the P content, the average cooling rate ofabout 50° C./min in a temperature range from 530° C. to 450° C. in theprocess of cooling after hot extrusion or hot forging was a boundaryvalue at which whether or not any P-containing compounds were observedin the metallographic structure at a magnification of 500-fold orwhether or not any P-containing compounds were observed with an electronmicroscope (Alloys Nos. S01, S02, and S51 to S66 subjected to theirrespective steps). When P-containing compounds were observed with ametallographic microscope, machinability was excellent. When the averagecooling rate in a temperature range from 530° C. to 450° C. was 0.2°C./min, it is presumed that strength slightly decreased, andmachinability slightly decreased because of a decrease in the amount ofβ phase and enlargement of P-containing compounds. However, bothstrength and machinability were at high levels (Step No. B2).

20) When P-containing compounds were not observed with a metallographicmicroscope but were observed with an electron microscope irrespective ofthe cooling rate and the P content, machinability was higher than whenno P-containing compounds were observed, achieving the target of theembodiments. However, the degree of improvement in machinability waslower than when P-containing compounds were observed with ametallographic microscope (Steps Nos. A1 and AH2, Steps Nos. F3 and FH2,for example, Alloy No. S63).

21) It was found that a bar prepared by performing low-temperatureannealing on a hot-worked material under the condition so that theannealing conditional expression f8 was 750 to 1485 was quite straightwith a bend of 0.1 mm or less for a length of one meter (Alloys Nos. S01and S02 and Steps Nos. A5, A6, and B6). An alloy in which γ phaseprecipitated by performing low-temperature annealing appeared. In analloy in which the amount of γ phase was about 1%, torque and turningperformance improved (for example, Alloys Nos. S01 and S02).

As described above, the alloys according to the embodiments in which thecontents of the respective additive elements, the composition relationalexpressions, and the respective metallographic structure relationalexpressions are in the appropriate ranges have excellent hot workability(in hot extrusion, hot forging, and hot rolling), and theirmachinability and mechanical characteristics are also good. Theexcellent properties in the alloys according to the embodiments can beobtained by adjusting the production conditions in hot extrusion, hotforging, and hot rolling as well as the heat treatment conditions suchthat they are within the appropriate ranges.

INDUSTRIAL APPLICABILITY

The free-cutting copper alloys according to the embodiments haveexcellent hot workability and machinability, high strength, andexcellent balance between strength and elongation although the amount ofPb contained is small. Therefore, the free-cutting copper alloysaccording to the embodiments are suitable for automobile components,electrical and electronic apparatus components, mechanical components,stationaries, toys, sliding components, measuring instrument components,precision mechanical components, medical components, drink-relateddevices and components, devices and components for water drainage,industrial plumbing components, and components relating to liquid or gassuch as drinking water, industrial water, drainage water, or hydrogen.

Specifically, the free-cutting copper alloys according to theembodiments are suitably applicable as a material that constitutes theitems used in the above-mentioned fields which go by the names includingvalve, joint, cock, faucet, gear, axle, bearing, shaft, sleeve, spindle,sensor, bolt, nut, flare nut, pen point, insert nut, cap nut, nipple,spacer, and screw.

1. A free-cutting copper alloy comprising: higher than 61.0 mass % andlower than 65.0 mass % of Cu; higher than 1.0 mass % and lower than 1.5mass % of Si; higher than or equal to 0.003 mass % and lower than 0.20mass % of Pb; and higher than 0.003 mass % and lower than 0.19 mass % ofP, with the balance being Zn and inevitable impurities, wherein amongthe inevitable impurities, a total content of Fe, Mn, Co, and Cr islower than 0.40 mass % and a total content of Sn and Al is lower than0.40 mass %, when a Cu content is represented by [Cu] mass %, a Sicontent is represented by [Si] mass %, a Pb content is represented by[Pb] mass %, and a P content is represented by [P] mass %, arelationship of 56.5 ≤ f 1 = [Cu] − 4.5 × [Si] + 0.5 × [Pb] − [P] ≤ 59.5is satisfied, in constituent phases of a metallographic structureexcluding non-metallic inclusions, among 10 metallic phases consistingof α phase, β phase, γ phase, δ phase, ε phase, ζ phase, η phase, κphase, μ phase, and χ phase, when an area ratio of α phase isrepresented by (α)%, an area ratio of γ phase is represented by (γ)%, anarea ratio of β phase is represented by (β)%, an area ratio of μ phaseis represented by (μ)%, an area ratio of κ phase is represented by (κ)%,an area ratio of δ phase is represented by (δ)%, an area ratio of εphase is represented by (ε)%, an area ratio of ζ phase is represented by(ζ)%, an area ratio of η phase is represented by (η)%, and an area ratioof χ phase is represented by (χ)%, providing that(α)+(β)+(γ)+(μ)+(κ)+(δ)+(ε)+(ζ)+(η)+(χ)=100, relationships of20 ≤ (α) ≤ 80, 15 ≤ (β) ≤ 80, 0 ≤ (γ) < 8, 18 × (γ)/(β) < 9, 20 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) ≤ 88, and  33 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) + ([Pb])^(1/2) × 35 + ([P])^(1/2) × 15are satisfied, and a P-containing compound having a grain size of 3 μmor less in diameter which can be observed at least in an examinationusing an electron microscope at a magnification of 2000 times is presentin the β phase.
 2. A free-cutting copper alloy comprising: higher thanor equal to 61.7 mass % and lower than or equal to 64.3 mass % of Cu;higher than or equal to 1.02 mass % and lower than or equal to 1.35 mass% of Si; higher than or equal to 0.005 mass % and lower than or equal to0.10 mass % of Pb; and higher than or equal to 0.02 mass % and lowerthan or equal to 0.14 mass % of P, with the balance being Zn andinevitable impurities, wherein among the inevitable impurities, a totalcontent of Fe, Mn, Co, and Cr is lower than or equal to 0.30 mass % anda total content of Sn and Al is lower than or equal to 0.30 mass %, whena Cu content is represented by [Cu] mass %, a Si content is representedby [Si] mass %, a Pb content is represented by [Pb] mass %, and a Pcontent is represented by [P] mass %, a relationship of57.0 ≤ f 1 = [Cu] − 4.5 × [Si] + 0.5 × [Pb] − [P] ≤ 59.0 is satisfied,in constituent phases of a metallographic structure excludingnon-metallic inclusions, among 10 metallic phases consisting of α phase,β phase, γ phase, δ phase, ε phase, ζ phase, η phase, κ phase, μ phase,and χ phase, when an area ratio of α phase is represented by (α)%, anarea ratio of γ phase is represented by (γ)%, an area ratio of β phaseis represented by (β)%, an area ratio of μ phase is represented by (μ)%,an area ratio of κ phase is represented by (κ)%, an area ratio of δphase is represented by (δ)%, an area ratio of ε phase is represented by(ε)%, an area ratio of ζ phase is represented by (ζ)%, an area ratio ofη phase is represented by (η)%, and an area ratio of χ phase isrepresented by (χ)%, providing that(α)+(β)+(γ)+(μ)+(κ)+(δ)+(ε)+(ζ)+(η)+(χ)=100, relationships of30 ≤ (α) ≤ 75, 25 ≤ (β) ≤ 70, 0 ≤ (γ) < 4, 18 × (γ)/(β) < 2, 30 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) ≤ 77, and44 ≤ (γ)^(1/2) × 3 + (β) × ([Si])^(1/2) + ([Pb])^(1/2) × 35 + ([P])^(1/2) × 15are satisfied, and a P-containing compound having a grain size of 3 μmor less in diameter which can be observed at least in an examinationusing an electron microscope at a magnification of 2000 times is presentin the β phase.
 3. The free-cutting copper alloy according to claim 1,wherein a proportion of a number of granular α phase crystal grainshaving an aspect ratio (longer side/shorter side) of lower than or equalto 4 to an entire number of α phase crystal grains is higher than orequal to 50%.
 4. The free-cutting copper alloy according to claim 1,wherein a Si content in β phase is higher than or equal to 1.2 mass %and lower than or equal to 1.9 mass %.
 5. The free-cutting copper alloyaccording to claim 1, wherein an electrical conductivity is higher thanor equal to 13% IACS, and when a tensile strength is represented by S(N/mm²) and an elongation is represented by E (%), a relationalexpression S×(100+E)/100 indicating a balance between the strength andthe elongation is higher than or equal to
 600. 6. The free-cuttingcopper alloy according to claim 1, which is used for an automobilecomponent, an electrical or electronic apparatus component, a mechanicalcomponent, a stationery, a toy, a sliding component, a measuringinstrument component, a precision mechanical component, a medicalcomponent, a drink-related device or component, a device or componentfor water drainage, or an industrial plumbing component.
 7. A method forproducing the free-cutting copper alloy according to claim 1, the methodcomprising: one or more hot working steps, wherein in the final hotworking step among the hot working steps, hot working temperature ishigher than 540° C. and lower than 675° C., and an average cooling ratein a temperature range from 530° C. to 450° C. after hot working ishigher than or equal to 0.1° C./min and lower than or equal to 50°C./min.
 8. The method for producing a free-cutting copper alloyaccording to claim 7, further comprising one or more steps selected froma cold working step, a straightness correction step, and an annealingstep.
 9. The method for producing a free-cutting copper alloy accordingto claim 7, further comprising a low-temperature annealing step that isperformed after the final step of processing, wherein in thelow-temperature annealing step, holding temperature is higher than orequal to 250° C. and lower than or equal to 430° C., and holding time islonger than or equal to 10 minutes and shorter than or equal to 200minutes.